SKU
Stock keeping unit
A SKU is a seller’s own code for one product it stocks, down to the size and colour, used to track stock and match rows between systems.
- Stock code
What it means
SKU stands for stock keeping unit. Shopify describes one as “an alphanumeric code created internally by sellers to identify, receive, and locate their product inventory”.1 Each size and colour gets its own, and WooCommerce wants every variation row to have “its own unique SKU”.2
Because each seller chooses its own, a SKU means nothing outside the system it was made for. A supplier’s SKU is a key into the supplier’s system, and yours is a key into yours.
Stores still lean on it. WooCommerce’s importer “uses product IDs or SKUs in the CSV to match existing products”.2 Google recommends your SKU as a product’s ID in Merchant Center.3 Shopify treats ABC123 and abc123 as two different SKUs.4
Think of it like this
A cloakroom ticket works the same way. It finds your coat at once in that cloakroom, and means nothing at the one next door.
For example
A supplier sends a hoodie as HD-200. In your shop the medium navy one becomes HD-200-NVY-M and the large grey one HD-200-GRY-L. Each size and colour can then be stocked, sold and reordered on its own.
Why it matters
On a repeat import, WooCommerce finds existing products by ID or SKU. So the code must not change between deliveries: WooCommerce’s advice is to “keep stable IDs or SKUs”.2 Spaces cause trouble too. In structured data, Google says “The sku value must not contain any whitespace characters”.5
Not to be confused with
A SKU is not a barcode number. A GTIN comes from the manufacturer and is the same in every shop, while your SKU is yours alone. Google says not to put internal SKUs in its GTIN, brand or MPN fields.6
Sources
- Shopify UK. What Is a Stock Keeping Unit (SKU)? Complete 2026 Guide.
- WooCommerce documentation. Product CSV Importer and Exporter.
- Google Merchant Center Help. ID [id].
- Shopify Help Center. Using SKUs to manage your inventory.
- Google Search Central. Merchant listing (Product, Offer) structured data.
- Google Merchant Center Help. About unique product identifiers.