What is a SKU?
A SKU, or stock keeping unit, is a unique code a retailer creates to identify and track one specific sellable version of a product. It is internal to the business: the brand invents the code, controls its format, and uses it across inventory systems, point of sale, warehouse management, and ecommerce platforms. A SKU does not just label a style. It labels an exact variant, so a black T-shirt in size medium and the same shirt in size large are two different SKUs even though they share a product name.
This is the difference between a SKU and a barcode. A UPC or EAN is a standardized number registered globally and shared across every retailer that sells that item. A SKU belongs to one company and is meaningful only inside that company's systems. A fashion brand might sell a dress that carries a single manufacturer UPC per variant while internally tracking it under its own SKU scheme that encodes season, category, and colorway.
How a SKU is structured
SKU codes are usually 8 to 12 alphanumeric characters built from segments that each describe a product attribute. A common practice is to start broad and narrow down, so the code reads as a hierarchy. For example, TOP-WOM-BLU-M-CTN could mean a top, women's, blue, medium, cotton. Another brand might use WREN101REDSM where WREN is the label, 101 is the sweatshirt category, RED is the color, and SM is the size.
Two rules keep a SKU system usable. Codes should be human-readable enough that a warehouse picker can sanity-check them, and they should avoid characters that confuse people or software, like the letter O next to the number 0. Most teams also avoid starting a SKU with the manufacturer name alone, since that produces long shared prefixes that slow visual scanning.
Why fashion needs many SKUs per style
Apparel multiplies fast. One style in five sizes and four colors is 20 SKUs. Add a petite and a tall length and the count doubles again. Each of those variants has its own stock level, its own sell-through, and its own reorder decision, which is why fashion catalogs run into thousands of SKUs even for a small brand.
- Inventory accuracy: stock counts only mean something at the variant level, not the style level.
- Reordering: a brand restocks the size and color that sold, not the whole style blindly.
- Analytics: sell-through and margin are measured per SKU to find winners and dead stock.
- Fulfillment: pick, pack, and ship workflows route on the SKU, not the marketing name.
SKUs on the product page
On an ecommerce product detail page, the SKU links the variant a shopper selects to the right inventory record and the right image. When a customer picks size large in green, the page should resolve to the green large SKU, show its stock status, and ideally show that exact colorway worn rather than a generic shot. Brands that map distinct on-model imagery to each colorway SKU give shoppers a more accurate picture, which tends to reduce returns driven by color or fit surprises.
Why SKUs matter for fashion brands and ecommerce
A clean SKU structure is the backbone of merchandising decisions. Buyers plan assortments by SKU, finance tracks margin by SKU, and operations forecasts demand by SKU. When the coding is inconsistent or duplicated, those reports break down: a best-selling color can look like a slow style because its sales are split across mismatched codes, and reorders go to the wrong variants.
The cost of getting it wrong rises with catalog size. A brand with 200 styles and a sloppy scheme might absorb the confusion manually. A brand syncing 5,000 variants across a website, a marketplace, and a 3PL cannot. Designing the SKU format before launch, and never reusing a retired code for a new product, prevents most of the data problems that surface later.
Practical takeaway
Define a SKU pattern that encodes category, style, color, and size in a fixed order, keep it consistent across every system, and treat each variant as its own tracked unit. Pair each colorway SKU with imagery that shows that exact variant so the product page matches what ships.