SKU in one sentence
A SKU is the identity of a sellable product variant in your systems. Every difference that matters to the customer or the warehouse – size, colour, model, pack size – usually means a separate SKU.
SKU vs barcode vs item number
| Identifier | Who sets it | What it is for |
|---|---|---|
| SKU | You (the goods owner) | Unique internal key for a product variant in your webshop, ERP and the warehouse system. |
| Barcode (EAN/GTIN) | Issued under the GS1 system | Global, machine-readable product identity printed on the product. See barcodes: EAN, GTIN and SSCC. |
| Supplier's article number | Your supplier | Useful on purchase orders, but should not replace your own SKU. |
In a 3PL setup, the SKU is the key that connects your webshop order, the warehouse location and the scanned barcode. If the keys do not match, orders cannot be allocated to stock. See connecting your webshop to a 3PL.
Units of measure and packaging levels
The same product can be handled in different units:
| Level | Example | Typical use |
|---|---|---|
| Each (EA) | One bottle | Consumer orders, small-item picking |
| Inner pack | 6 bottles in a shrink-wrapped pack | Retail-ready units |
| Case / master carton | 4 inner packs = 24 bottles | Inbound deliveries, B2B orders |
| Pallet | 40 cartons on a EUR pallet | Bulk storage, full-pallet B2B orders |
The unit of measure (UOM) tells the system which level a quantity refers to, and the case pack tells it how many units a carton holds. If the system does not know that a carton holds 24 units, a B2B order for "2 cartons" and an ecommerce order for "2 bottles" cannot be handled from the same stock. See B2B vs B2C logistics.
Good SKU practice
- One SKU per sellable variant – no shared SKUs for different sizes or colours.
- Stable and unique – never reuse an old SKU for a new product.
- Simple characters – letters, digits and hyphens are safest across systems.
- Complete master data – barcode, weight, dimensions and packaging levels for every SKU.
- One master system – decide whether the ERP, the webshop or a PIM owns item data.
SKU data a 3PL warehouse needs
Before goods arrive, the warehouse needs an item register with SKU, product name, barcode, weight, dimensions, packaging levels (units per carton and per pallet) and any special requirements such as batch tracking or expiry dates. At Karlholm Logistics item data is set up in Ongoing WMS during onboarding, and every movement is then scanned against it.
Frequently asked questions
Is a SKU the same as a barcode?
No. The SKU is your own internal identifier for a product variant. The barcode (often an EAN/GTIN) is a machine-readable code printed on the product. A good item register links each SKU to its barcode.
Can a SKU be reused for a new product?
It should not be. Reusing a SKU links old stock, orders and history to the wrong product and causes errors in integrations.
Do bundles and kits need their own SKU?
Usually yes. A kit gets its own SKU, and the warehouse system needs to know which component SKUs it consumes.
Short definitions in the glossary: SKU – Stock Keeping Unit · EA – Each · Case · Case pack · Inner pack · Master carton · UOM – Unit of Measure
This page gives general information about logistics terms. It is not legal, customs or tax advice, and it does not describe the terms of any specific agreement with Karlholm Logistics.