What an SKU identifies
A stock keeping unit is the code your business uses for one specific thing a customer can buy. Not the product family — the exact version. A jacket sold in three sizes and two colours is one product and six SKUs, because those six are counted, picked and reordered separately.
An SKU is yours. You invent the format, and it usually encodes something readable to staff such as a brand, a category, a size and a colour. That makes it different from a manufacturer part number, which the maker assigns, and from a barcode identifier such as a GTIN, which is global and identifies the same item wherever it is sold. A shop generally holds all three, and they are not interchangeable.
Why SKUs matter for marketing
The SKU is the thread that ties everything together. Stock levels, order lines, returns, shopping feeds, analytics reports and ad performance all hang off it. When the code is consistent, you can ask which exact variant sells, which one is returned most often and which one is quietly out of stock while advertising continues to run.
It matters most in shopping and catalogue advertising, where the feed sends one row per sellable variant. If the identifier in that feed does not match the identifier in the shop and in analytics, the numbers stop reconciling and nobody can say which variant earned the revenue. Getting product IDs stable and consistent is dull work that pays for itself the first time you have to explain a report.
Common mistakes with SKUs
Changing them is the expensive one. Renaming an SKU during a redesign, a platform move or a supplier change looks harmless, but it resets the item’s history in ads and analytics, orphans reviews attached to the old code, and can force shopping platforms to relearn the item from scratch. Treat an SKU as permanent for the life of the item.
Reusing a retired code for a new product is the same mistake with an extra problem, because old orders and new orders then share an identifier and the data silently mixes.
The last is granularity. Giving every variant its own SKU is correct; inventing separate SKUs for the same item sold on different channels is not, because the same jacket then appears as two products and the stock figure for each is wrong.
How to act on it
Agree one format and one owner before the catalogue grows. A readable, consistent pattern is worth more than a clever one, and someone has to be responsible for issuing codes so two people do not invent different ones for the same item.
Then make the shop, the feed and the analytics use the same identifier for the same thing, and check it periodically rather than assuming. If a supplier change means an item genuinely becomes a different product, give it a new code and retire the old one properly instead of editing the record in place. Keep variant data attached to the SKU too, so size and colour can be reported on without guesswork.