What is SKU (Stock Keeping Unit)?

In short

An SKU (stock keeping unit) is your own internal code for one exact product variant — a specific colour and size, not just the product. It is how your store, your warehouse and your accounting system agree on which item was sold, picked and invoiced.

How to build an SKU system

A workable SKU is short, readable and built from stable attributes: category, model, colour, size. TSHIRT-BLK-M tells a picker what to fetch without opening the admin. Avoid spaces, accented characters and symbols that break in spreadsheets or CSV imports.

Keep the structure identical across the whole catalogue and never reuse a retired code for a different product. Historical reports, returns and supplier records all point back to that code, and reusing it quietly corrupts a year of data.

An SKU is not a barcode. The EAN or GTIN is a global identifier from the manufacturer, used by marketplaces and shopping feeds; the SKU is yours. Most stores need both, stored in separate fields so each system reads the right one.

Why it matters for an online store in the EU

As soon as you sell in more than one channel or ship from an external warehouse, the SKU becomes the shared language. Marketplaces, courier integrations and accounting tools all reconcile against it, and an inconsistent code turns every stock check into manual work.

A practical example: a clothing store adds a new colour. With a clear structure the new variants follow the same pattern and appear correctly in the warehouse and in the shopping feed the same day. With ad-hoc codes, someone ends up mapping them by hand every month — and eventually ships the wrong size.

Common mistakes

Using the supplier's code, which changes without warning and differs between suppliers.
One SKU for a whole product instead of one per variant.
Spaces, accents or slashes that break CSV imports and integrations.
Reusing the code of a discontinued product for a new item.
Encoding the price or a promotion in the SKU, which then has to change.

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Frequently asked questions about SKUs

What should an SKU contain?

Stable attributes only: category or model, then the variant details such as colour and size. Keep it short enough to read aloud, uppercase, with hyphens instead of spaces. Anything that can change — price, supplier, campaign — belongs in its own field, never inside the code itself.

What is the difference between SKU and barcode?

The SKU is your internal code and you decide its format. A barcode, usually an EAN or GTIN, is a global identifier issued for the product and used by marketplaces and shopping feeds. Store them in separate fields, because different systems expect different identifiers.

Can I change SKUs later?

You can, but it costs. Old orders, supplier documents and reports keep the previous code, so a rename means mapping old to new everywhere. If the current system is unusable, migrate once, document the mapping, and keep the new structure fixed from then on.