SKU

A Stock Keeping Unit is the code you use inside your own business to identify and track one specific sellable item. You assign it yourself, you decide how it is structured, and it only has to be unique within your own catalogue. A typical SKU might look like "TSHIRT-RED-L" or "1042-BLK-42" — anything that lets your systems and staff recognise the exact variant at a glance.

This is the defining contrast with a GTIN. A GTIN is issued by GS1, is globally unique, and is shared by everyone who handles that product. An SKU is the opposite: it is private, self-assigned, and meaningless to anyone outside your operation. Two different shops can use the SKU "001" for completely different products, and that is perfectly fine because the SKU never leaves your own system.

A common point of confusion is that an SKU and a GTIN often map one-to-one — each variant has both. But they exist for different reasons. The GTIN identifies what the product is to the outside world; the SKU identifies how you stock and fulfil it internally. A single GTIN-carrying product still needs an SKU so your warehouse and accounting systems can track it.

SKUs should always be assigned at the variant level. If you sell a t-shirt in three sizes and four colours, that is twelve sellable variants, and each needs its own SKU (and ideally its own GTIN). Assigning one SKU to the whole product line makes inventory counts and reorder points meaningless, because you cannot tell which size or colour is actually selling.

A well-designed SKU encodes useful information in a consistent order — for example category, then product, then attributes like size and colour. Keep it human-readable, avoid easily confused characters such as the letter O and the number 0, and never reuse a retired SKU for a different product. Consistency matters more than cleverness: every team member should be able to read an SKU the same way.

On marketplaces, the SKU is the field that ties your published listing back to your internal stock and orders. When inventory and price sync runs across several channels, it matches on the SKU you assigned to each listing, so keeping SKUs stable and consistent across platforms is what makes reliable multichannel sync possible. Change an SKU carelessly and you can break the link between a live listing and its stock count.