Refactor production and stock tests to remove UOM dependency

- Updated production.spec.ts, stock-adjustments.spec.ts, and stock-transfers.spec.ts to eliminate UOM references in API seeder and test cases.
- Adjusted ApiSeeder methods to remove UOM parameters from stock receiving and production template creation.
- Revised documentation to reflect changes in UOM handling, emphasizing that stock is counted in base UOM only.
- Introduced new enums for MeasureUnit and StageQtyUnit to clarify content size and stage input quantities.
- Implemented ItemContent service to validate and normalize content sizes.
- Updated smoke tests to validate production stage inputs expressed in content units, ensuring correct consumption calculations.
- Modified frontend UOM label handling to reflect the removal of per-line UOMs in document lines.

Backend/ERPCore/Services/BundleSaleService.cs

@@ -19,11 +19,9 @@ public sealed class BundleSaleService : IBundleSaleService
     private readonly IRepository<BundleSale> _bundles;
     private readonly IRepository<Customer> _customers;
     private readonly IRepository<Item> _items;
-    private readonly IRepository<Uom> _uoms;
     private readonly IRepository<Warehouse> _warehouses;
     private readonly IRepository<User> _users;
     private readonly ISalesDomainService _sales;
-    private readonly IUomConverter _uomConverter;
     private readonly ISalesPostingService _posting;
     private readonly ICurrentUser _currentUser;
     private readonly INumberSequenceService _numbers;
@@ -34,11 +32,9 @@ public sealed class BundleSaleService : IBundleSaleService
         IRepository<BundleSaleTemplate> templates,
         IRepository<Customer> customers,
         IRepository<Item> items,
-        IRepository<Uom> uoms,
         IRepository<Warehouse> warehouses,
         IRepository<User> users,
         ISalesDomainService sales,
-        IUomConverter uomConverter,
         ISalesPostingService posting,
         ICurrentUser currentUser,
         INumberSequenceService numbers,
@@ -48,11 +44,9 @@ public sealed class BundleSaleService : IBundleSaleService
         _bundles = bundles;
         _customers = customers;
         _items = items;
-        _uoms = uoms;
         _warehouses = warehouses;
         _users = users;
         _sales = sales;
-        _uomConverter = uomConverter;
         _posting = posting;
         _currentUser = currentUser;
         _numbers = numbers;
@@ -85,7 +79,7 @@ public sealed class BundleSaleService : IBundleSaleService
             template.CreatedAt,
             template.UpdatedAt,
             template.Lines.OrderBy(x => x.SortOrder).Select(x => new BundleSaleTemplateLineDto(
-                x.BundleSaleTemplateLineId, x.ItemId, x.UomId, x.WarehouseId, x.Qty, x.UnitPrice, x.IncludeInBundle, x.SortOrder)).ToList());
+                x.BundleSaleTemplateLineId, x.ItemId, x.WarehouseId, x.Qty, x.UnitPrice, x.IncludeInBundle, x.SortOrder)).ToList());
     }
 
     public async Task<PagedResponse<BundleSaleSummaryDto>> ListAsync(PageQuery query, BundleSaleStatus? status, int? customerId, int? warehouseId, CancellationToken ct = default)
@@ -196,7 +190,6 @@ public sealed class BundleSaleService : IBundleSaleService
             : template.Lines.OrderBy(x => x.SortOrder).Select(x => new CreateBundleSaleTemplateLineRequest
             {
                 ItemId = x.ItemId,
-                UomId = x.UomId,
                 WarehouseId = x.WarehouseId,
                 Qty = x.Qty,
                 UnitPrice = x.UnitPrice,
@@ -214,17 +207,15 @@ public sealed class BundleSaleService : IBundleSaleService
             var lineWarehouseId = warehouseId;
 
             var item = await _items.Query().AsNoTracking().FirstAsync(x => x.ItemId == r.ItemId, ct);
-            await _sales.ValidateSalesLineAsync(warehouseId, r.ItemId, r.UomId, lineWarehouseId, r.Qty, 0m, null, ct);
-            var (qtyBase, unitCostBase) = await _uomConverter.ToBaseAsync(item, r.UomId, r.Qty, r.UnitPrice, ct);
-            var calc = _sales.ComputeLine(qtyBase, 0m, unitCostBase, SalesDiscountMode.Amount, 0m, 0m, 0m, 0m, false);
+            await _sales.ValidateSalesLineAsync(warehouseId, r.ItemId, lineWarehouseId, r.Qty, 0m, null, ct);
+            var calc = _sales.ComputeLine(r.Qty, 0m, r.UnitPrice, SalesDiscountMode.Amount, 0m, 0m, 0m, 0m, false);
             lines.Add(new BundleSaleLine
             {
                 ItemId = r.ItemId,
                 Description = item.Name,
-                Qty = qtyBase,
-                UomId = item.BaseUomId,
+                Qty = r.Qty,
                 WarehouseId = lineWarehouseId,
-                UnitPrice = unitCostBase,
+                UnitPrice = r.UnitPrice,
                 LineTotal = calc.LineTotal,
                 IncludeInBundle = r.IncludeInBundle,
                 IsComponent = true,
@@ -251,6 +242,6 @@ public sealed class BundleSaleService : IBundleSaleService
         x.BundleSaleId, x.BundleNo, x.BundleDate, x.CustomerId, x.CustomerSnapshotName, x.WarehouseId, x.CashierUserId, x.BundleSaleTemplateId,
         x.BundleName, x.BundleCode, x.Status, x.ComponentSubtotal, x.BundlePrice, x.MarginAmount, x.DiscountTotal, x.TaxTotal, x.GrandTotal,
         x.CreatedAt, x.UpdatedAt,
-        x.Lines.Select(l => new BundleSaleLineDto(l.BundleSaleLineId, l.ItemId, l.Description, l.Qty, l.UomId, l.WarehouseId, l.UnitPrice, l.LineTotal, l.IncludeInBundle, l.IsComponent, l.ParentLineId)).ToList());
+        x.Lines.Select(l => new BundleSaleLineDto(l.BundleSaleLineId, l.ItemId, l.Description, l.Qty, l.WarehouseId, l.UnitPrice, l.LineTotal, l.IncludeInBundle, l.IsComponent, l.ParentLineId)).ToList());
 
 }

Backend/ERPCore/Services/GrnService.cs

@@ -28,14 +28,12 @@ public sealed class GrnService : IGrnService
     private readonly IRepository<PurchaseOrder> _pos;
     private readonly IRepository<PoLine> _poLines;
     private readonly IRepository<Item> _items;
-    private readonly IRepository<Uom> _uoms;
     private readonly IRepository<Warehouse> _warehouses;
     private readonly IRepository<Bin> _bins;
     private readonly IRepository<Vendor> _vendors;
     private readonly IRepository<Batch> _batches;
     private readonly IRepository<StockLayer> _layers;
     private readonly IRepository<StockLedger> _ledger;
-    private readonly IUomConverter _uomConverter;
     private readonly IFifoCostingService _fifo;
     private readonly INumberSequenceService _numbers;
     private readonly ICurrentUser _currentUser;
@@ -43,23 +41,21 @@ public sealed class GrnService : IGrnService
 
     public GrnService(
         IRepository<Grn> grns, IRepository<PurchaseOrder> pos, IRepository<PoLine> poLines,
-        IRepository<Item> items, IRepository<Uom> uoms, IRepository<Warehouse> warehouses,
+        IRepository<Item> items, IRepository<Warehouse> warehouses,
         IRepository<Bin> bins, IRepository<Vendor> vendors, IRepository<Batch> batches,
-        IRepository<StockLayer> layers, IRepository<StockLedger> ledger, IUomConverter uomConverter,
+        IRepository<StockLayer> layers, IRepository<StockLedger> ledger,
         IFifoCostingService fifo, INumberSequenceService numbers, ICurrentUser currentUser, IUnitOfWork uow)
     {
         _grns = grns;
         _pos = pos;
         _poLines = poLines;
         _items = items;
-        _uoms = uoms;
         _warehouses = warehouses;
         _bins = bins;
         _vendors = vendors;
         _batches = batches;
         _layers = layers;
         _ledger = ledger;
-        _uomConverter = uomConverter;
         _fifo = fifo;
         _numbers = numbers;
         _currentUser = currentUser;
@@ -133,8 +129,6 @@ public sealed class GrnService : IGrnService
         {
             var item = await _items.Query().AsNoTracking().FirstOrDefaultAsync(i => i.ItemId == input.ItemId, ct)
                 ?? throw new DomainException(ErrorCodes.Validation, $"Item {input.ItemId} does not exist.", 422);
-            if (!await _uoms.Query().AnyAsync(u => u.UomId == input.UomId, ct))
-                throw new DomainException(ErrorCodes.Validation, $"UOM {input.UomId} does not exist.", 422);
             if (input.BinId is not null && !await _bins.Query().AnyAsync(b => b.BinId == input.BinId && b.WarehouseId == request.WarehouseId, ct))
                 throw new DomainException(ErrorCodes.Validation, $"Bin {input.BinId} is not in warehouse {request.WarehouseId}.", 422);
 
@@ -150,6 +144,8 @@ public sealed class GrnService : IGrnService
                 if (poLine.ItemId != input.ItemId)
                     throw new DomainException(ErrorCodes.Validation, $"PO line {input.PoLineId} is for a different item.", 422);
 
+                // Both sides are counts of the item's base UOM — the GRN line no longer carries
+                // a unit of its own — so this comparison and the accrual below are like-for-like.
                 var openQty = poLine.Qty - poLine.QtyReceived;
                 if (input.Qty > openQty * (1 + OverReceiptTolerance))
                     throw new DomainException(ErrorCodes.OverReceiptTolerance,
@@ -174,7 +170,6 @@ public sealed class GrnService : IGrnService
             {
                 PoLineId = input.PoLineId,
                 ItemId = input.ItemId,
-                UomId = input.UomId,
                 BinId = input.BinId,
                 Batch = batch, // navigation so EF fixes up BatchId once the batch is inserted
                 Qty = input.Qty,
@@ -234,10 +229,11 @@ public sealed class GrnService : IGrnService
         {
             foreach (var line in grn.Lines.OrderBy(l => l.GrnLineId))
             {
-                var item = await _items.Query().AsNoTracking().FirstAsync(i => i.ItemId == line.ItemId, token);
                 // FIFO layer costs at the after-discount net price; VAT is recoverable and never
-                // enters stock value (docs/10 FR-GRN-06, revised).
-                var (qtyBase, unitCostBase) = await ToBaseAsync(item, line.UomId, line.Qty, line.NetUnitCost, token);
+                // enters stock value (docs/10 FR-GRN-06, revised). The line quantity is already
+                // a count of the item's base UOM, so it layers exactly as entered.
+                var qtyBase = line.Qty;
+                var unitCostBase = line.NetUnitCost;
 
                 var layer = await _fifo.CreateInboundLayerAsync(
                     line.ItemId, grn.WarehouseId, line.BatchId, null, line.GrnLineId,
@@ -345,15 +341,6 @@ public sealed class GrnService : IGrnService
         return created; // linked via GrnLine.Batch navigation; FK fixed up on SaveChanges
     }
 
-    /// <summary>
-    /// Delegates to the shared <see cref="IUomConverter"/>. This was a private method here
-    /// until manufacturing needed the same conversion for stage stock inputs; behaviour is
-    /// identical, so receive costing is unchanged.
-    /// </summary>
-    private Task<(decimal QtyBase, decimal UnitCostBase)> ToBaseAsync(
-        Item item, int uomId, decimal qty, decimal unitCostPerUom, CancellationToken ct)
-        => _uomConverter.ToBaseAsync(item, uomId, qty, unitCostPerUom, ct);
-
     private async Task UpdatePoStatusAsync(int? poId, CancellationToken ct)
     {
         if (poId is null) return;
@@ -392,7 +379,7 @@ public sealed class GrnService : IGrnService
     private static GrnDto Map(Grn g) => new(
         g.GrnId, g.DocNo, g.PoId, g.VendorId, g.WarehouseId, g.Status, g.CreatedBy, g.CreatedAt, g.PostedAt,
         g.Lines.OrderBy(l => l.GrnLineId).Select(l => new GrnLineDto(
-            l.GrnLineId, l.PoLineId, l.ItemId, l.UomId, l.BinId, l.Qty, l.UnitCost, l.PoUnitPrice,
+            l.GrnLineId, l.PoLineId, l.ItemId, l.BinId, l.Qty, l.UnitCost, l.PoUnitPrice,
             l.DiscountPct, l.NetUnitCost, l.VatPct, l.VatAmount, l.ReceivedValue, l.LineTotal,
             l.PoUnitPrice is null ? 0m : Math.Round((l.UnitCost - l.PoUnitPrice.Value) * l.Qty, 4, MidpointRounding.AwayFromZero),
             l.HoldStatus, l.BatchId)).ToList());

Backend/ERPCore/Services/Interfaces/IItemMeasure.cs

@@ -0,0 +1,25 @@
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+
+namespace ERPCore.Services.Interfaces;
+
+/// <summary>
+/// Resolves a production formula quantity to the only unit stock speaks: a count of the
+/// item's base UOM. Replaces the old per-item UOM conversion table — everything needed is
+/// on the item row, so this does no I/O.
+/// </summary>
+public interface IItemMeasure
+{
+    /// <summary>
+    /// Formula quantity → packs. <see cref="StageQtyUnit.Pack"/> passes straight through;
+    /// <see cref="StageQtyUnit.Content"/> divides by the item's content size, so 2000 ml of
+    /// a 500 ml bottle is 4 bottles and 300 ml is 0.6 of one.
+    /// </summary>
+    decimal ToPacks(Item item, decimal formulaQty, StageQtyUnit unit);
+
+    /// <summary>Packs → formula quantity. The exact inverse of <see cref="ToPacks"/>, for display.</summary>
+    decimal FromPacks(Item item, decimal packs, StageQtyUnit unit);
+
+    /// <summary>Whether the item carries a usable content size.</summary>
+    bool HasContent(Item item);
+}

Backend/ERPCore/Services/Interfaces/IItemService.cs

@@ -24,6 +24,4 @@ public interface IItemService
     Task SetStatusAsync(int itemId, EntityStatus status, CancellationToken ct = default);
 
     Task<ItemReorderSettingsDto> UpdateReorderAsync(int itemId, UpdateReorderRequest request, CancellationToken ct = default);
-
-    Task<ItemUomConversionsDto> UpdateUomConversionsAsync(int itemId, UpdateUomConversionsRequest request, CancellationToken ct = default);
 }

Backend/ERPCore/Services/Interfaces/ISalesDomainService.cs

@@ -15,7 +15,6 @@ public interface ISalesDomainService
     Task ValidateSalesLineAsync(
         int headerWarehouseId,
         int lineItemId,
-        int lineUomId,
         int lineWarehouseId,
         decimal qty,
         decimal freeQty,

Backend/ERPCore/Services/Interfaces/IUomConverter.cs

@@ -1,35 +0,0 @@
-using ERPCore.Domain.Entities;
-
-namespace ERPCore.Services.Interfaces;
-
-/// <summary>
-/// Converts a quantity and its per-UOM cost into the item's <b>base</b> UOM.
-/// </summary>
-/// <remarks>
-/// <para>Everything in the FIFO engine — <c>StockLayer</c>, <c>StockLedger</c>,
-/// <c>IFifoCostingService.ConsumeAsync</c> — works exclusively in base UOM, while
-/// documents let a user enter a line in any UOM the item has a conversion for. This is the
-/// one place that bridges the two.</para>
-/// <para>Extracted from <c>GrnService</c>'s private <c>ToBaseAsync</c> when manufacturing
-/// needed the same conversion for stage stock inputs (docs/30 never mentions UOM
-/// conversion, but <c>STAGE_INPUT.uom_id</c> is a free FK — without this, an input
-/// specified in "Box of 12" would consume 1 base unit instead of 12 and silently
-/// mis-cost the run).</para>
-/// </remarks>
-public interface IUomConverter
-{
-    /// <summary>
-    /// Returns the quantity and unit cost restated in <paramref name="item"/>'s base UOM.
-    /// A no-op when <paramref name="uomId"/> already is the base UOM. Throws 422 when no
-    /// conversion is defined for the item from that UOM to its base.
-    /// </summary>
-    Task<(decimal QtyBase, decimal UnitCostBase)> ToBaseAsync(
-        Item item, int uomId, decimal qty, decimal unitCostPerUom, CancellationToken ct = default);
-
-    /// <summary>
-    /// Quantity-only conversion, for callers that have no per-UOM cost to restate (a
-    /// production stage input declares a quantity; its cost comes from the FIFO layers it
-    /// consumes, not from the document).
-    /// </summary>
-    Task<decimal> ToBaseQtyAsync(Item item, int uomId, decimal qty, CancellationToken ct = default);
-}

Backend/ERPCore/Services/ItemContent.cs

@@ -0,0 +1,61 @@
+using ERPCore.Domain.Enums;
+using ERPCore.System.Errors;
+
+namespace ERPCore.Services;
+
+/// <summary>
+/// Item content-size rules: validate the (qty, unit) pair and normalise it to a base
+/// unit. Pure — no DI, no database — because everything it needs is on the item row.
+/// <para>
+/// Litres and kilograms exist only at the point of entry. Everything stored and every
+/// downstream calculation works in millilitres or grams, so no consumer ever has to ask
+/// which unit it is holding.
+/// </para>
+/// </summary>
+public static class ItemContent
+{
+    /// <summary>
+    /// Rejects a half-filled pair. Both null is valid and means "this item has no
+    /// measurable content" — a screw, a label, a service.
+    /// </summary>
+    public static void ValidatePair(decimal? contentQty, MeasureUnit? contentUnit)
+    {
+        if (contentQty is null && contentUnit is null) return;
+
+        if (contentQty is null || contentUnit is null)
+            throw new DomainException(
+                ErrorCodes.Validation,
+                "contentQty and contentUnit must be supplied together, or both left null.", 422);
+
+        if (contentQty <= 0)
+            throw new DomainException(
+                ErrorCodes.Validation, "contentQty must be greater than zero.", 422);
+    }
+
+    /// <summary>
+    /// Converts an entered content size to its base unit: L → Ml and Kg → G, both ×1000;
+    /// Ml and G pass through. Both-null in, both-null out.
+    /// <para>
+    /// Rounded to 4dp AwayFromZero to match the quantity columns' <c>(18,4)</c> scale and
+    /// <c>ProductionRunService.Scale</c>, so a content size can never carry precision the
+    /// database would silently drop.
+    /// </para>
+    /// </summary>
+    public static (decimal? BaseQty, MeasureUnit? BaseUnit) Normalize(
+        decimal? contentQty, MeasureUnit? contentUnit)
+    {
+        if (contentQty is null || contentUnit is null) return (null, null);
+
+        var (factor, baseUnit) = contentUnit.Value switch
+        {
+            MeasureUnit.Ml => (1m, MeasureUnit.Ml),
+            MeasureUnit.L => (1000m, MeasureUnit.Ml),
+            MeasureUnit.G => (1m, MeasureUnit.G),
+            MeasureUnit.Kg => (1000m, MeasureUnit.G),
+            _ => throw new DomainException(
+                ErrorCodes.Validation, $"Unsupported content unit '{contentUnit}'.", 422)
+        };
+
+        return (Math.Round(contentQty.Value * factor, 4, MidpointRounding.AwayFromZero), baseUnit);
+    }
+}

Backend/ERPCore/Services/ItemService.cs

@@ -31,6 +31,8 @@ public sealed class ItemService : IItemService
     private readonly IRepository<Uom> _uoms;
     private readonly IRepository<Vendor> _vendors;
     private readonly IRepository<Warehouse> _warehouses;
+    private readonly IRepository<StockLayer> _stockLayers;
+    private readonly IRepository<StockLedger> _stockLedger;
     private readonly IProductConfigService _config;
     private readonly IUnitOfWork _uow;
 
@@ -42,6 +44,8 @@ public sealed class ItemService : IItemService
         IRepository<Uom> uoms,
         IRepository<Vendor> vendors,
         IRepository<Warehouse> warehouses,
+        IRepository<StockLayer> stockLayers,
+        IRepository<StockLedger> stockLedger,
         IProductConfigService config,
         IUnitOfWork uow)
     {
@@ -52,6 +56,8 @@ public sealed class ItemService : IItemService
         _uoms = uoms;
         _vendors = vendors;
         _warehouses = warehouses;
+        _stockLayers = stockLayers;
+        _stockLedger = stockLedger;
         _config = config;
         _uow = uow;
     }
@@ -79,7 +85,9 @@ public sealed class ItemService : IItemService
             .Select(i => new ItemListItemDto(
                 i.ItemId, i.Sku, i.Name, i.CategoryId, i.SubCategoryId, i.BrandId,
                 i.BaseUomId, i.DefaultVendorId,
-                i.StockNature, i.TrackingMode, i.TaxClass, i.SalePrice, i.Status))
+                i.StockNature, i.TrackingMode, i.TaxClass, i.SalePrice,
+                i.ContentQty, i.ContentUnit, i.ContentBaseQty, i.ContentBaseUnit,
+                i.Status))
             .ToListAsync(ct);
 
         return PagedResponse<ItemListItemDto>.Create(rows, query.Page, query.PageSize, total);
@@ -89,7 +97,6 @@ public sealed class ItemService : IItemService
     {
         var item = await _items.Query().AsNoTracking()
             .Include(i => i.ReorderSettings)
-            .Include(i => i.UomConversions)
             .FirstOrDefaultAsync(i => i.ItemId == itemId, ct);
 
         return item is null ? null : new ETagged<ItemDetailDto>(ToDetail(item), item.RowVersion);
@@ -104,6 +111,9 @@ public sealed class ItemService : IItemService
             request.CategoryId, request.SubCategoryId, request.BrandId,
             request.BaseUomId, request.DefaultVendorId, ct);
 
+        ItemContent.ValidatePair(request.ContentQty, request.ContentUnit);
+        var (contentBaseQty, contentBaseUnit) = ItemContent.Normalize(request.ContentQty, request.ContentUnit);
+
         var item = new Item
         {
             Sku = request.Sku.Trim(),
@@ -118,6 +128,10 @@ public sealed class ItemService : IItemService
             TrackingMode = request.TrackingMode,
             TaxClass = request.TaxClass,
             SalePrice = request.SalePrice,
+            ContentQty = request.ContentQty,
+            ContentUnit = request.ContentUnit,
+            ContentBaseQty = contentBaseQty,
+            ContentBaseUnit = contentBaseUnit,
             Status = EntityStatus.Active,
             CreatedAt = DateTime.UtcNow
         };
@@ -133,7 +147,6 @@ public sealed class ItemService : IItemService
     {
         var item = await _items.Query()
             .Include(i => i.ReorderSettings)
-            .Include(i => i.UomConversions)
             .FirstOrDefaultAsync(i => i.ItemId == itemId, ct)
             ?? throw new NotFoundException($"Item {itemId} was not found.");
 
@@ -148,6 +161,18 @@ public sealed class ItemService : IItemService
             request.CategoryId, request.SubCategoryId, request.BrandId,
             request.BaseUomId, request.DefaultVendorId, ct);
 
+        // The base UOM is the sole meaning of every quantity recorded against this item —
+        // stock layers, ledger rows and document lines are all plain counts of it. Once any
+        // of that history exists, changing it would silently reinterpret every one of those
+        // numbers (240 bottles becoming 240 cases), so it is frozen instead.
+        if (item.BaseUomId != request.BaseUomId && await HasStockHistoryAsync(itemId, ct))
+            throw new DomainException(
+                ErrorCodes.MasterInUse,
+                $"Item {itemId} has stock history; its base UOM can no longer be changed.", 409);
+
+        ItemContent.ValidatePair(request.ContentQty, request.ContentUnit);
+        var (contentBaseQty, contentBaseUnit) = ItemContent.Normalize(request.ContentQty, request.ContentUnit);
+
         item.Sku = request.Sku.Trim();
         item.Name = request.Name.Trim();
         item.Description = request.Description;
@@ -160,6 +185,10 @@ public sealed class ItemService : IItemService
         item.TrackingMode = request.TrackingMode;
         item.TaxClass = request.TaxClass;
         item.SalePrice = request.SalePrice;
+        item.ContentQty = request.ContentQty;
+        item.ContentUnit = request.ContentUnit;
+        item.ContentBaseQty = contentBaseQty;
+        item.ContentBaseUnit = contentBaseUnit;
         item.UpdatedAt = DateTime.UtcNow;
 
         await SaveGuardingConcurrencyAsync(ct);
@@ -224,52 +253,14 @@ public sealed class ItemService : IItemService
         return new ItemReorderSettingsDto(settings);
     }
 
-    public async Task<ItemUomConversionsDto> UpdateUomConversionsAsync(
-        int itemId, UpdateUomConversionsRequest request, CancellationToken ct = default)
-    {
-        var pairs = request.Conversions.Select(c => (c.FromUom, c.ToUom)).ToList();
-        if (pairs.Distinct().Count() != pairs.Count)
-            throw new DomainException(ErrorCodes.Validation, "Duplicate (fromUom, toUom) in conversions.", 400);
-
-        var item = await _items.Query()
-            .Include(i => i.UomConversions)
-            .FirstOrDefaultAsync(i => i.ItemId == itemId, ct)
-            ?? throw new NotFoundException($"Item {itemId} was not found.");
-
-        foreach (var uomId in request.Conversions.SelectMany(c => new[] { c.FromUom, c.ToUom }).Distinct())
-            if (!await _uoms.Query().AnyAsync(u => u.UomId == uomId, ct))
-                throw new DomainException(ErrorCodes.Validation, $"UOM {uomId} does not exist.", 422);
-
-        foreach (var stale in item.UomConversions.Where(c => request.Conversions.All(r => r.FromUom != c.FromUomId || r.ToUom != c.ToUomId)).ToList())
-            item.UomConversions.Remove(stale);
-        foreach (var input in request.Conversions)
-        {
-            var existing = item.UomConversions.FirstOrDefault(c => c.FromUomId == input.FromUom && c.ToUomId == input.ToUom);
-            if (existing is null)
-            {
-                item.UomConversions.Add(new UomConversion
-                {
-                    ItemId = itemId,
-                    FromUomId = input.FromUom,
-                    ToUomId = input.ToUom,
-                    Factor = input.Factor
-                });
-            }
-            else
-            {
-                existing.Factor = input.Factor;
-            }
-        }
-
-        item.UpdatedAt = DateTime.UtcNow;
-        await _uow.SaveChangesAsync(ct);
-
-        var conversions = item.UomConversions
-            .OrderBy(c => c.ConversionId)
-            .Select(c => new UomConversionDto(c.ConversionId, c.FromUomId, c.ToUomId, c.Factor))
-            .ToList();
-        return new ItemUomConversionsDto(item.ItemId, item.BaseUomId, conversions);
-    }
+    /// <summary>
+    /// Whether anything has ever been recorded against this item's stock. Checks the ledger
+    /// as well as live layers, because a fully consumed item has no layer left but its
+    /// history still reads in the old unit.
+    /// </summary>
+    private async Task<bool> HasStockHistoryAsync(int itemId, CancellationToken ct)
+        => await _stockLayers.Query().AnyAsync(l => l.ItemId == itemId, ct)
+           || await _stockLedger.Query().AnyAsync(l => l.ItemId == itemId, ct);
 
     /// <summary>
     /// Validates every FK on an item write, and gates the optional ones on the product
@@ -350,14 +341,12 @@ public sealed class ItemService : IItemService
     private static ItemDetailDto ToDetail(Item i) => new(
         i.ItemId, i.Sku, i.Name, i.Description, i.CategoryId, i.SubCategoryId, i.BrandId,
         i.BaseUomId, i.DefaultVendorId,
-        i.StockNature, i.TrackingMode, i.TaxClass, i.SalePrice, i.Status,
+        i.StockNature, i.TrackingMode, i.TaxClass, i.SalePrice,
+        i.ContentQty, i.ContentUnit, i.ContentBaseQty, i.ContentBaseUnit,
+        i.Status,
         i.ReorderSettings
             .OrderBy(r => r.WarehouseId)
             .Select(r => new ItemReorderDto(r.WarehouseId, r.ReorderPoint, r.ReorderQty))
             .ToList(),
-        i.UomConversions
-            .OrderBy(c => c.ConversionId)
-            .Select(c => new UomConversionDto(c.ConversionId, c.FromUomId, c.ToUomId, c.Factor))
-            .ToList(),
         i.CreatedAt, i.UpdatedAt);
 }

Backend/ERPCore/Services/Production/ProductionGraphValidator.cs

@@ -21,9 +21,10 @@ namespace ERPCore.Services.Production;
 /// </remarks>
 public static class ProductionGraphValidator
 {
-    public sealed record InputDraft(int Index, StageInputSource Source, int? ItemId, string? FromOutputKey);
+    public sealed record InputDraft(
+        int Index, StageInputSource Source, int? ItemId, string? FromOutputKey, StageQtyUnit QtyUnit);
 
-    public sealed record OutputDraft(string Key, string Name, int? ItemId);
+    public sealed record OutputDraft(string Key, string Name, int? ItemId, int? UomId);
 
     public sealed record StageDraft(
         string Key, string Name, IReadOnlyList<InputDraft> Inputs, IReadOnlyList<OutputDraft> Outputs);
@@ -171,6 +172,12 @@ public static class ProductionGraphValidator
                         throw new DomainException(ErrorCodes.GraphInputSourceInvalid,
                             $"Input {input.Index + 1} of stage '{s.Name}' is a Stock input and cannot reference an upstream output.", 422);
                 }
+
+                // WIP has no content size — it is counted in whatever unit its source output
+                // declares — so only a Stock input may be expressed in ml/g.
+                if (input.Source == StageInputSource.Upstream && input.QtyUnit != StageQtyUnit.Pack)
+                    throw new DomainException(ErrorCodes.GraphInputSourceInvalid,
+                        $"Input {input.Index + 1} of stage '{s.Name}' is Upstream, so its quantity must be in whole units of its source output, not content units.", 422);
             }
         }
 
@@ -189,6 +196,20 @@ public static class ProductionGraphValidator
             foreach (var o in s.Outputs.Where(o => o.ItemId is not null))
                 throw Invalid(
                     $"Output '{o.Name}' of stage '{s.Name}' is intermediate work-in-progress and cannot reference an item — only the final stage produces a stocked item.");
+
+        // 7 — output units. An item-bearing output already has a unit (the item's base UOM),
+        // so carrying a second one could only contradict it. WIP has no item to ask, so it
+        // must name its own — the label the run board and any downstream input display.
+        foreach (var s in stages)
+            foreach (var o in s.Outputs)
+            {
+                if (o.ItemId is null && o.UomId is null)
+                    throw new DomainException(ErrorCodes.WipUnitRequired,
+                        $"Output '{o.Name}' of stage '{s.Name}' is work-in-progress and must declare a unit.", 422);
+                if (o.ItemId is not null && o.UomId is not null)
+                    throw Invalid(
+                        $"Output '{o.Name}' of stage '{s.Name}' references an item, so its unit comes from that item and must not be set.");
+            }
     }
 
     /// <summary>Set of keys reachable from <paramref name="roots"/> following <paramref name="next"/>.</summary>

Backend/ERPCore/Services/Production/ProductionRunService.cs

@@ -26,7 +26,7 @@ public sealed class ProductionRunService : IProductionRunService
     private readonly IRepository<Item> _items;
     private readonly IRepository<ReasonCode> _reasonCodes;
     private readonly IFifoCostingService _fifo;
-    private readonly IUomConverter _uomConverter;
+    private readonly IItemMeasure _measure;
     private readonly INumberSequenceService _numbers;
     private readonly IUnitOfWork _uow;
     private readonly ICurrentUser _currentUser;
@@ -35,7 +35,7 @@ public sealed class ProductionRunService : IProductionRunService
         IRepository<ProductionRun> runs, IRepository<ProductionTemplate> templates,
         IRepository<Warehouse> warehouses, IRepository<Bin> bins,
         IRepository<Item> items, IRepository<ReasonCode> reasonCodes,
-        IFifoCostingService fifo, IUomConverter uomConverter,
+        IFifoCostingService fifo, IItemMeasure measure,
         INumberSequenceService numbers, IUnitOfWork uow, ICurrentUser currentUser)
     {
         _runs = runs;
@@ -45,7 +45,7 @@ public sealed class ProductionRunService : IProductionRunService
         _items = items;
         _reasonCodes = reasonCodes;
         _fifo = fifo;
-        _uomConverter = uomConverter;
+        _measure = measure;
         _numbers = numbers;
         _uow = uow;
         _currentUser = currentUser;
@@ -245,7 +245,7 @@ public sealed class ProductionRunService : IProductionRunService
                     Source = i.Source,
                     ItemId = i.ItemId,
                     FromRunOutput = i.FromOutputId is null ? null : outputByTemplateOutputId[i.FromOutputId.Value],
-                    UomId = i.UomId,
+                    QtyUnit = i.QtyUnit,
                     PlannedQty = Scale(i.QtyPerBatch, ratio)
                 });
             }
@@ -367,9 +367,11 @@ public sealed class ProductionRunService : IProductionRunService
                     ?? throw new DomainException(ErrorCodes.Validation,
                         $"Item {input.ItemId} on stage '{stage.Name}' no longer exists.", 422);
 
-                // PlannedQty is in the input's declared UOM; ConsumedQty is in the item's
-                // base UOM (the only unit FIFO and the ledger speak). Compare in base.
-                var plannedBase = await _uomConverter.ToBaseQtyAsync(item, input.UomId, input.PlannedQty, token);
+                // PlannedQty is in the input's declared unit — content (ml/g) for an item with
+                // a content size, otherwise packs. ConsumedQty is always packs, the only unit
+                // FIFO and the ledger speak, so resolve before comparing. 2000 ml of a 500 ml
+                // bottle is 4 bottles; 300 ml is 0.6 of one, which (18,4) stores exactly.
+                var plannedBase = _measure.ToPacks(item, input.PlannedQty, input.QtyUnit);
                 var delta = plannedBase - input.ConsumedQty;
                 if (delta <= 0) continue; // rework restart with no increase — nothing to draw
 
@@ -1057,7 +1059,9 @@ public sealed class ProductionRunService : IProductionRunService
                 $"Item {item.Sku} is {item.TrackingMode}-tracked; batch/serial-tracked finished goods "
                 + "are not supported in this phase.", 422);
 
-        var qtyBase = await _uomConverter.ToBaseQtyAsync(item, output.UomId, good, ct);
+        // Output quantities are always a count of the finished item's base UOM — produced and
+        // scrapped are recorded in whole bottles, not millilitres — so nothing to resolve.
+        var qtyBase = good;
 
         var consumedValue = run.Stages.SelectMany(s => s.Inputs).Sum(i => i.ConsumedValue);
         var returnedValue = run.Stages.SelectMany(s => s.Inputs).Sum(i => i.ReturnedValue);
@@ -1223,7 +1227,7 @@ public sealed class ProductionRunService : IProductionRunService
                 ProductionJson.Deserialize<List<FieldDefDto>>(s.FieldDefs, []),
                 ParseJson(s.FieldValues),
                 s.Inputs.OrderBy(i => i.RunInputId).Select(i => new RunStageInputDto(
-                    i.RunInputId, i.Source, i.ItemId, i.FromRunOutputId, i.UomId,
+                    i.RunInputId, i.Source, i.ItemId, i.FromRunOutputId, i.QtyUnit,
                     i.PlannedQty, i.ConsumedQty, i.ConsumedValue,
                     i.DeliveredQty, i.ReturnedQty, i.ReturnedValue)).ToList(),
                 s.Outputs.OrderBy(o => o.RunOutputId).Select(o => new RunStageOutputDto(

Backend/ERPCore/Services/Production/ProductionTemplateService.cs

@@ -253,19 +253,20 @@ public sealed class ProductionTemplateService : IProductionTemplateService
         ProductionGraphValidator.Validate(
             request.Stages.Select(s => new ProductionGraphValidator.StageDraft(
                 s.Key, s.Name,
-                s.Inputs.Select((i, idx) => new ProductionGraphValidator.InputDraft(idx, i.Source, i.ItemId, i.FromOutputKey)).ToList(),
-                s.Outputs.Select(o => new ProductionGraphValidator.OutputDraft(o.Key, o.Name, o.ItemId)).ToList())).ToList(),
+                s.Inputs.Select((i, idx) => new ProductionGraphValidator.InputDraft(idx, i.Source, i.ItemId, i.FromOutputKey, i.QtyUnit)).ToList(),
+                s.Outputs.Select(o => new ProductionGraphValidator.OutputDraft(o.Key, o.Name, o.ItemId, o.UomId)).ToList())).ToList(),
             request.Edges.Select(e => new ProductionGraphValidator.EdgeDraft(e.ParentKey, e.ChildKey)).ToList());
 
         var itemIds = request.Stages
             .SelectMany(s => s.Inputs.Select(i => i.ItemId).Concat(s.Outputs.Select(o => o.ItemId)))
             .OfType<int>().Distinct().ToList();
 
+        var contentByItem = new Dictionary<int, decimal?>();
         if (itemIds.Count > 0)
         {
             var found = await _items.Query().AsNoTracking()
                 .Where(i => itemIds.Contains(i.ItemId))
-                .Select(i => new { i.ItemId, i.Status })
+                .Select(i => new { i.ItemId, i.Status, i.ContentBaseQty })
                 .ToListAsync(ct);
 
             var missing = itemIds.Except(found.Select(f => f.ItemId)).ToList();
@@ -277,19 +278,42 @@ public sealed class ProductionTemplateService : IProductionTemplateService
             if (inactive.Count > 0)
                 throw new DomainException(ErrorCodes.Validation,
                     $"Item(s) {string.Join(", ", inactive)} are inactive and cannot be used in a template.", 422);
+
+            contentByItem = found.ToDictionary(f => f.ItemId, f => f.ContentBaseQty);
         }
 
+        // A Content quantity is only meaningful against an item that declares a content size,
+        // and it must still land on a storable pack count: quantities persist at (18,4), so
+        // anything under 0.0001 packs would round to zero and consume nothing at stage start.
+        foreach (var s in request.Stages)
+            foreach (var i in s.Inputs.Where(i => i.QtyUnit == StageQtyUnit.Content))
+            {
+                var contentBaseQty = contentByItem.GetValueOrDefault(i.ItemId ?? 0);
+                if (contentBaseQty is not > 0m)
+                    throw new DomainException(ErrorCodes.Validation,
+                        $"Stage '{s.Name}' has an input in content units, but item {i.ItemId} has no content size.", 422);
+
+                if (i.QtyPerBatch / contentBaseQty.Value < 0.0001m)
+                    throw new DomainException(ErrorCodes.Validation,
+                        $"Stage '{s.Name}': {i.QtyPerBatch} is less than 0.0001 of item {i.ItemId}'s content size ({contentBaseQty}), which would round to no stock at all.", 422);
+            }
+
+        // Only WIP outputs carry a UOM now; the validator has already rejected one on an
+        // item-bearing output, so every non-null id here belongs to real work-in-progress.
         var uomIds = request.Stages
-            .SelectMany(s => s.Inputs.Select(i => i.UomId).Concat(s.Outputs.Select(o => o.UomId)))
-            .Distinct().ToList();
+            .SelectMany(s => s.Outputs.Select(o => o.UomId))
+            .OfType<int>().Distinct().ToList();
 
-        var knownUoms = await _uoms.Query().AsNoTracking()
-            .Where(u => uomIds.Contains(u.UomId)).Select(u => u.UomId).ToListAsync(ct);
+        if (uomIds.Count > 0)
+        {
+            var knownUoms = await _uoms.Query().AsNoTracking()
+                .Where(u => uomIds.Contains(u.UomId)).Select(u => u.UomId).ToListAsync(ct);
 
-        var missingUoms = uomIds.Except(knownUoms).ToList();
-        if (missingUoms.Count > 0)
-            throw new DomainException(ErrorCodes.Validation,
-                $"UOM(s) {string.Join(", ", missingUoms)} do not exist.", 422);
+            var missingUoms = uomIds.Except(knownUoms).ToList();
+            if (missingUoms.Count > 0)
+                throw new DomainException(ErrorCodes.Validation,
+                    $"UOM(s) {string.Join(", ", missingUoms)} do not exist.", 422);
+        }
 
         // Annotations go into jsonb unvalidated by anything else, so pin the one field the
         // client renders off. Unknown kinds would round-trip fine but draw nothing.
@@ -428,7 +452,7 @@ public sealed class ProductionTemplateService : IProductionTemplateService
                     Source = i.Source,
                     ItemId = i.Source == StageInputSource.Stock ? i.ItemId : null,
                     FromOutput = i.Source == StageInputSource.Upstream ? outputsByKey[i.FromOutputKey!] : null,
-                    UomId = i.UomId,
+                    QtyUnit = i.QtyUnit,
                     QtyPerBatch = i.QtyPerBatch
                 });
             }
@@ -476,7 +500,7 @@ public sealed class ProductionTemplateService : IProductionTemplateService
                 s.Inputs.OrderBy(i => i.InputId).Select(i => new StageInputDto(
                     i.InputId, i.Source, i.ItemId, i.FromOutputId,
                     i.FromOutputId is null ? null : outputKeyById.GetValueOrDefault(i.FromOutputId.Value),
-                    i.UomId, i.QtyPerBatch)).ToList(),
+                    i.QtyUnit, i.QtyPerBatch)).ToList(),
                 s.Outputs.OrderBy(o => o.OutputId).Select(o => new StageOutputDto(
                     o.OutputId, o.OutputId.ToString(), o.ItemId, o.Name, o.UomId, o.QtyPerBatch)).ToList()))
             .ToList();

Backend/ERPCore/Services/PurchaseOrderService.cs

@@ -222,7 +222,6 @@ public sealed class PurchaseOrderService : IPurchaseOrderService
     private static PoLine ToLine(CreatePoLineInput l) => new()
     {
         ItemId = l.ItemId,
-        UomId = l.UomId,
         WarehouseId = l.WarehouseId,
         Qty = l.Qty,
         UnitPrice = l.UnitPrice,
@@ -258,7 +257,6 @@ public sealed class PurchaseOrderService : IPurchaseOrderService
             throw new DomainException(ErrorCodes.Validation, $"Requisition {requisitionId} does not exist.", 422);
 
         await EnsureAllExistAsync(_items.Query().Select(i => i.ItemId), lines.Select(l => l.ItemId), "Item", ct);
-        await EnsureAllExistAsync(_uoms.Query().Select(u => u.UomId), lines.Select(l => l.UomId), "UOM", ct);
         await EnsureAllExistAsync(_warehouses.Query().Select(w => w.WarehouseId), lines.Select(l => l.WarehouseId), "Warehouse", ct);
     }
 
@@ -276,5 +274,5 @@ public sealed class PurchaseOrderService : IPurchaseOrderService
         p.PoId, p.DocNo, p.VendorId, p.RequisitionId, p.Status, p.ApprovalRequired,
         p.CreatedBy, p.CreatedAt, p.UpdatedAt, ComputeTotals(p.Lines),
         p.Lines.OrderBy(l => l.PoLineId).Select(l => new PoLineDto(
-            l.PoLineId, l.ItemId, l.UomId, l.WarehouseId, l.Qty, l.UnitPrice, l.Tax, l.QtyReceived)).ToList());
+            l.PoLineId, l.ItemId, l.WarehouseId, l.Qty, l.UnitPrice, l.Tax, l.QtyReceived)).ToList());
 }

Backend/ERPCore/Services/SalesDomainService.cs

@@ -13,7 +13,6 @@ public sealed class SalesDomainService : ISalesDomainService
     private readonly IRepository<Warehouse> _warehouses;
     private readonly IRepository<User> _users;
     private readonly IRepository<Item> _items;
-    private readonly IRepository<Uom> _uoms;
     private readonly ISalesPricingService _pricing;
 
     public SalesDomainService(
@@ -21,14 +20,12 @@ public sealed class SalesDomainService : ISalesDomainService
         IRepository<Warehouse> warehouses,
         IRepository<User> users,
         IRepository<Item> items,
-        IRepository<Uom> uoms,
         ISalesPricingService pricing)
     {
         _customers = customers;
         _warehouses = warehouses;
         _users = users;
         _items = items;
-        _uoms = uoms;
         _pricing = pricing;
     }
 
@@ -48,7 +45,7 @@ public sealed class SalesDomainService : ISalesDomainService
     }
 
     public async Task ValidateSalesLineAsync(
-        int headerWarehouseId, int lineItemId, int lineUomId, int lineWarehouseId, decimal qty, decimal freeQty, int? parentLineId, CancellationToken ct = default)
+        int headerWarehouseId, int lineItemId, int lineWarehouseId, decimal qty, decimal freeQty, int? parentLineId, CancellationToken ct = default)
     {
         if (qty <= 0)
             throw new DomainException(ErrorCodes.Validation, "Sales line quantity must be greater than zero.", 422);
@@ -60,8 +57,6 @@ public sealed class SalesDomainService : ISalesDomainService
             throw new DomainException(ErrorCodes.Validation, $"Sales line warehouse {lineWarehouseId} must match header warehouse {headerWarehouseId}.", 422);
         if (!await _items.Query().AnyAsync(x => x.ItemId == lineItemId, ct))
             throw new NotFoundException($"Item {lineItemId} was not found.");
-        if (!await _uoms.Query().AnyAsync(x => x.UomId == lineUomId, ct))
-            throw new NotFoundException($"UOM {lineUomId} was not found.");
         if (!await _warehouses.Query().AnyAsync(x => x.WarehouseId == lineWarehouseId, ct))
             throw new NotFoundException($"Warehouse {lineWarehouseId} was not found.");
     }

Backend/ERPCore/Services/SalesInvoiceService.cs

@@ -145,7 +145,7 @@ public sealed class SalesInvoiceService : ISalesInvoiceService
         foreach (var r in requests)
         {
             var item = await _items.Query().AsNoTracking().FirstAsync(x => x.ItemId == r.ItemId, ct);
-            await _sales.ValidateSalesLineAsync(headerWarehouseId, r.ItemId, r.UomId, r.WarehouseId, r.Qty, r.FreeQty, r.ParentLineId, ct);
+            await _sales.ValidateSalesLineAsync(headerWarehouseId, r.ItemId, r.WarehouseId, r.Qty, r.FreeQty, r.ParentLineId, ct);
             var resolved = await _sales.ResolveLinePriceAsync(r.ItemId, r.WarehouseId, r.UnitPrice, r.AllowManualPriceOverride, ct);
             var unitPrice = resolved.UnitPrice;
             var priceSource = resolved.PriceSource;
@@ -158,7 +158,6 @@ public sealed class SalesInvoiceService : ISalesInvoiceService
                 Description = item.Name,
                 Qty = r.Qty,
                 FreeQty = r.FreeQty,
-                UomId = r.UomId,
                 WarehouseId = r.WarehouseId,
                 UnitPrice = unitPrice,
                 BaseCost = unitPrice,

Backend/ERPCore/Services/SalesMappingService.cs

@@ -35,7 +35,7 @@ public sealed class SalesMappingService : ISalesMappingService
             invoice.InvoiceType, invoice.Status, invoice.CreatedBy, invoice.CreatedAt, invoice.UpdatedAt,
             MapInvoiceTotals(invoice),
             invoice.Lines.Select(l => new SalesInvoiceLineDto(
-                l.SalesInvoiceLineId, l.ItemId, l.Description, l.Qty, l.FreeQty, l.UomId, l.WarehouseId,
+                l.SalesInvoiceLineId, l.ItemId, l.Description, l.Qty, l.FreeQty, l.WarehouseId,
                 l.UnitPrice, l.BaseCost, l.PriceSource, l.DiscountPct, l.DiscountAmount, l.DiscountMode,
                 l.NetUnitPrice, l.LineTotal, l.TaxPct, l.TaxAmount, l.IsFreeIssue, l.ParentLineId)).ToList());
 
@@ -45,7 +45,7 @@ public sealed class SalesMappingService : ISalesMappingService
             slip.WarehouseId, slip.CashierUserId, slip.Status, slip.CreatedAt, slip.UpdatedAt,
             MapSlipTotals(slip),
             slip.Lines.Select(l => new SalesSlipLineDto(
-                l.SalesSlipLineId, l.ItemId, l.Description, l.Qty, l.FreeQty, l.UomId, l.WarehouseId,
+                l.SalesSlipLineId, l.ItemId, l.Description, l.Qty, l.FreeQty, l.WarehouseId,
                 l.UnitPrice, l.BaseCost, l.PriceSource, l.DiscountPct, l.DiscountAmount, l.DiscountMode,
                 l.NetUnitPrice, l.LineTotal, l.TaxPct, l.TaxAmount, l.IsFreeIssue, l.ParentLineId)).ToList());
 }

Backend/ERPCore/Services/SalesPostingService.cs

@@ -20,7 +20,6 @@ public sealed class SalesPostingService : ISalesPostingService
     private readonly IRepository<Item> _items;
     private readonly IFifoCostingService _fifo;
     private readonly ISalesDomainService _sales;
-    private readonly IUomConverter _uomConverter;
     private readonly ICurrentUser _currentUser;
     private readonly IUnitOfWork _uow;
 
@@ -31,7 +30,6 @@ public sealed class SalesPostingService : ISalesPostingService
         IRepository<Item> items,
         IFifoCostingService fifo,
         ISalesDomainService sales,
-        IUomConverter uomConverter,
         ICurrentUser currentUser,
         IUnitOfWork uow)
     {
@@ -41,7 +39,6 @@ public sealed class SalesPostingService : ISalesPostingService
         _items = items;
         _fifo = fifo;
         _sales = sales;
-        _uomConverter = uomConverter;
         _currentUser = currentUser;
         _uow = uow;
     }
@@ -141,7 +138,7 @@ public sealed class SalesPostingService : ISalesPostingService
             notFoundMessage: $"Sales invoice {salesInvoiceId} was not found.",
             statusSelector: x => x.Status,
             ensureDraftMessage: x => $"Sales invoice {x.SalesInvoiceId} is {x.Status} and cannot be posted.",
-            getLines: x => x.Lines.Select(l => new PostingLine(l.ItemId, l.WarehouseId, l.UomId, l.Qty + l.FreeQty, l.Qty, l.FreeQty)),
+            getLines: x => x.Lines.Select(l => new PostingLine(l.ItemId, l.WarehouseId, l.Qty + l.FreeQty, l.Qty, l.FreeQty)),
             setPosted: x => x.Status = SalesInvoiceStatus.Posted,
             setUpdated: x => x.UpdatedAt = DateTime.UtcNow,
             sourceDocType: DocumentTypes.SalesInvoice,
@@ -154,7 +151,7 @@ public sealed class SalesPostingService : ISalesPostingService
             notFoundMessage: $"Sales slip {salesSlipId} was not found.",
             statusSelector: x => x.Status,
             ensureDraftMessage: x => $"Sales slip {x.SalesSlipId} is {x.Status} and cannot be posted.",
-            getLines: x => x.Lines.Select(l => new PostingLine(l.ItemId, l.WarehouseId, l.UomId, l.Qty + l.FreeQty, l.Qty, l.FreeQty)),
+            getLines: x => x.Lines.Select(l => new PostingLine(l.ItemId, l.WarehouseId, l.Qty + l.FreeQty, l.Qty, l.FreeQty)),
             setPosted: x => x.Status = SalesSlipStatus.Posted,
             setUpdated: x => x.UpdatedAt = DateTime.UtcNow,
             sourceDocType: DocumentTypes.SalesSlip,
@@ -167,9 +164,7 @@ public sealed class SalesPostingService : ISalesPostingService
             notFoundMessage: $"Bundle sale {bundleSaleId} was not found.",
             statusSelector: x => x.Status,
             ensureDraftMessage: x => $"Bundle sale {x.BundleSaleId} is {x.Status} and cannot be posted.",
-            // Bundle lines are normalized to base UOM on save, so posting should consume the
-            // stored base quantity directly instead of converting again.
-            getLines: x => x.Lines.Where(l => l.IncludeInBundle).Select(l => new PostingLine(l.ItemId, l.WarehouseId, l.UomId, l.Qty, l.Qty, 0m)),
+            getLines: x => x.Lines.Where(l => l.IncludeInBundle).Select(l => new PostingLine(l.ItemId, l.WarehouseId, l.Qty, l.Qty, 0m)),
             setPosted: x => x.Status = BundleSaleStatus.Posted,
             setUpdated: x => x.UpdatedAt = DateTime.UtcNow,
             sourceDocType: DocumentTypes.BundleSale,
@@ -203,6 +198,8 @@ public sealed class SalesPostingService : ISalesPostingService
                 if (!await _sales.IsStockedItemAsync(line.ItemId, token))
                     continue;
 
+                // Line quantities are already a count of the item's base UOM — sales documents
+                // carry no unit of their own — so this is the quantity FIFO consumes verbatim.
                 var consumed = await _fifo.ConsumeAsync(line.ItemId, line.WarehouseId, null, line.Qty, token);
                 var cost = consumed.Count == 0 ? 0m : consumed.Sum(x => x.Qty * x.UnitCost) / consumed.Sum(x => x.Qty);
                 await _fifo.PostLedgerAsync(line.ItemId, line.WarehouseId, null, null, null, _currentUser.AuditUserId,
@@ -214,5 +211,5 @@ public sealed class SalesPostingService : ISalesPostingService
         }, ct);
     }
 
-    private sealed record PostingLine(int ItemId, int WarehouseId, int UomId, decimal Qty, decimal PaidQty, decimal FreeQty);
+    private sealed record PostingLine(int ItemId, int WarehouseId, decimal Qty, decimal PaidQty, decimal FreeQty);
 }

Backend/ERPCore/Services/SalesSlipService.cs

@@ -169,7 +169,7 @@ public sealed class SalesSlipService : ISalesSlipService
         foreach (var r in requests)
         {
             var item = await _items.Query().AsNoTracking().FirstAsync(x => x.ItemId == r.ItemId, ct);
-            await _sales.ValidateSalesLineAsync(headerWarehouseId, r.ItemId, r.UomId, r.WarehouseId, r.Qty, r.FreeQty, r.ParentLineId, ct);
+            await _sales.ValidateSalesLineAsync(headerWarehouseId, r.ItemId, r.WarehouseId, r.Qty, r.FreeQty, r.ParentLineId, ct);
             var resolved = await _sales.ResolveLinePriceAsync(r.ItemId, r.WarehouseId, r.UnitPrice, r.AllowManualPriceOverride, ct);
             var unitPrice = resolved.UnitPrice;
             var priceSource = resolved.PriceSource;
@@ -182,7 +182,6 @@ public sealed class SalesSlipService : ISalesSlipService
                 Description = item.Name,
                 Qty = r.Qty,
                 FreeQty = r.FreeQty,
-                UomId = r.UomId,
                 WarehouseId = r.WarehouseId,
                 UnitPrice = unitPrice,
                 BaseCost = unitPrice,
@@ -222,8 +221,10 @@ public sealed class SalesSlipService : ISalesSlipService
             .Where(i => i.ItemId == line.ItemId)
             .Select(i => new { i.ItemId, i.Sku, i.Name, i.BaseUomId })
             .FirstOrDefault();
-        var uom = line is null ? null : _uoms.Query().AsNoTracking()
-            .Where(u => u.UomId == line.UomId)
+        // The line carries no unit of its own — its quantity is a count of the item's base
+        // UOM — so the display name comes from there.
+        var uom = item is null ? null : _uoms.Query().AsNoTracking()
+            .Where(u => u.UomId == item.BaseUomId)
             .Select(u => new { u.UomId, u.Name })
             .FirstOrDefault();
         var warehouse = _warehouses.Query().AsNoTracking()
@@ -240,8 +241,7 @@ public sealed class SalesSlipService : ISalesSlipService
             line?.ItemId ?? 0,
             item?.Sku ?? $"SKU-{line?.ItemId ?? 0}",
             item?.Name ?? line?.Description ?? "—",
-            line?.UomId ?? 0,
-            uom?.Name ?? $"UOM {line?.UomId ?? 0}",
+            uom?.Name ?? $"UOM {item?.BaseUomId ?? 0}",
             line?.Qty ?? 0m,
             line?.FreeQty ?? 0m,
             line is null ? "No line" : $"Buy {line.Qty} Get {line.FreeQty}");
@@ -263,7 +263,7 @@ public sealed class SalesSlipService : ISalesSlipService
             x.CreatedAt,
             x.UpdatedAt,
             summary,
-            x.Lines.Select(l => new SalesSlipLineDto(l.SalesSlipLineId, l.ItemId, l.Description, l.Qty, l.FreeQty, l.UomId, l.WarehouseId, l.UnitPrice, l.BaseCost, l.PriceSource, l.DiscountPct, l.DiscountAmount, l.DiscountMode, l.NetUnitPrice, l.LineTotal, l.TaxPct, l.TaxAmount, l.IsFreeIssue, l.ParentLineId)).ToList());
+            x.Lines.Select(l => new SalesSlipLineDto(l.SalesSlipLineId, l.ItemId, l.Description, l.Qty, l.FreeQty, l.WarehouseId, l.UnitPrice, l.BaseCost, l.PriceSource, l.DiscountPct, l.DiscountAmount, l.DiscountMode, l.NetUnitPrice, l.LineTotal, l.TaxPct, l.TaxAmount, l.IsFreeIssue, l.ParentLineId)).ToList());
     }
 
     private SalesSlipDto Map(SalesSlip x) => _mapping.MapSlip(x);

Backend/ERPCore/Services/Stock/ItemMeasure.cs

@@ -0,0 +1,39 @@
+using ERPCore.Domain.Entities;
+using ERPCore.Domain.Enums;
+using ERPCore.Services.Interfaces;
+using ERPCore.System.Errors;
+
+namespace ERPCore.Services.Stock;
+
+/// <summary>
+/// Content ↔ pack arithmetic (see <see cref="IItemMeasure"/>). Stateless and I/O-free:
+/// the content size is already on the <see cref="Item"/> every caller has loaded.
+/// </summary>
+public sealed class ItemMeasure : IItemMeasure
+{
+    public bool HasContent(Item item) => item.ContentBaseQty is > 0m;
+
+    public decimal ToPacks(Item item, decimal formulaQty, StageQtyUnit unit)
+    {
+        if (unit == StageQtyUnit.Pack) return formulaQty;
+
+        // Rounded to the quantity columns' (18,4) scale with the same mode as
+        // ProductionRunService.Scale, so what FIFO consumes and what the cost pool divides
+        // by are the same number to the last stored digit.
+        return Math.Round(formulaQty / RequireContent(item), 4, MidpointRounding.AwayFromZero);
+    }
+
+    public decimal FromPacks(Item item, decimal packs, StageQtyUnit unit)
+    {
+        if (unit == StageQtyUnit.Pack) return packs;
+
+        return Math.Round(packs * RequireContent(item), 4, MidpointRounding.AwayFromZero);
+    }
+
+    private static decimal RequireContent(Item item)
+        => item.ContentBaseQty is > 0m
+            ? item.ContentBaseQty.Value
+            : throw new DomainException(
+                ErrorCodes.Validation,
+                $"Item {item.ItemId} has no content size, so its quantity cannot be expressed in content units.", 422);
+}

Backend/ERPCore/Services/Stock/UomConverter.cs

@@ -1,38 +0,0 @@
-using ERPCore.Domain.Entities;
-using ERPCore.Repositories.Interfaces;
-using ERPCore.Services.Interfaces;
-using ERPCore.System.Errors;
-using Microsoft.EntityFrameworkCore;
-
-namespace ERPCore.Services.Stock;
-
-/// <summary>
-/// Shared UOM → base-UOM conversion (see <see cref="IUomConverter"/>). Behaviour is
-/// unchanged from the <c>GrnService.ToBaseAsync</c> it was extracted from, so the GRN
-/// receive path keeps costing exactly as before.
-/// </summary>
-public sealed class UomConverter : IUomConverter
-{
-    private readonly IRepository<UomConversion> _conversions;
-
-    public UomConverter(IRepository<UomConversion> conversions) => _conversions = conversions;
-
-    public async Task<(decimal QtyBase, decimal UnitCostBase)> ToBaseAsync(
-        Item item, int uomId, decimal qty, decimal unitCostPerUom, CancellationToken ct = default)
-    {
-        if (uomId == item.BaseUomId)
-            return (qty, unitCostPerUom);
-
-        var conv = await _conversions.Query().AsNoTracking()
-            .FirstOrDefaultAsync(c => c.ItemId == item.ItemId && c.FromUomId == uomId && c.ToUomId == item.BaseUomId, ct)
-            ?? throw new DomainException(ErrorCodes.Validation,
-                $"No UOM conversion from {uomId} to base UOM {item.BaseUomId} for item {item.ItemId}.", 422);
-
-        // Quantity scales up by the factor, so the per-unit cost scales down by it —
-        // total value is preserved.
-        return (qty * conv.Factor, unitCostPerUom / conv.Factor);
-    }
-
-    public async Task<decimal> ToBaseQtyAsync(Item item, int uomId, decimal qty, CancellationToken ct = default)
-        => (await ToBaseAsync(item, uomId, qty, 0m, ct)).QtyBase;
-}