Stock Keeping Unit (SKU)

Understanding Stock Keeping Unit (SKU)

Every unique product variant — a specific size, color, material, or configuration — gets its own SKU. A t-shirt available in three sizes and four colors has twelve SKUs, even though it is one product listing. SKUs are internal identifiers created by the merchant, distinct from universal product codes (UPCs) or manufacturer part numbers (MPNs) which are standardized across the industry.

A well-designed SKU system encodes useful information in the code itself. For example, "TS-BLU-M" might represent a t-shirt, blue, medium. This makes warehouse operations faster because pickers can identify products from the SKU without scanning barcodes. The structure should be consistent across your catalog: category, attribute, variant, in the same order every time.

SKU management becomes critical as catalog size grows. A store with 500 products averaging 5 variants each manages 2,500 SKUs. Tracking inventory, reorder points, and sales velocity at the SKU level ensures you never overstock slow-moving variants or run out of popular ones. SKU-level analytics also reveal which specific variants drive revenue and which sit as dead stock.

In Shopify, each product can have up to 100 variants, each with its own SKU. The SKU field is used for inventory tracking, order fulfillment, and integration with third-party logistics (3PL) providers and warehouse management systems. Clean, consistent SKU data is essential for any store that fulfills more than a handful of orders per day.