What is a SKU?

SKU Definition

A SKU (Stock Keeping Unit) is a unique identifier assigned to every distinct, sellable version of a product. Where a product describes what you sell, a SKU pinpoints exactly which one — down to the specific size, color, or configuration that gets picked, packed, and shipped.

A t-shirt in 3 colors and 4 sizes generates 12 SKUs — one per combination. Change the color, you change the SKU.

What's the difference between a SKU and a product?

A product is the general item — a Classic Crew Neck T-Shirt. A SKU is the exact, purchasable variant — Classic Crew Neck T-Shirt, Blue, Large. One product can have one SKU or hundreds, depending on how many variants it has. In most catalog systems, the product is the parent; SKUs are its children.

What's the difference between a SKU and an attribute?

Attributes describe a product; SKUs identify a specific version of it. Attributes are the building blocks and the SKU are what gets built from them: every unique combination of attributes becomes its own SKU.

A t-shirt has one Color attribute and one Size attribute, but a Blue Large and a Red Small are two different SKUs. Same attributes, different values, different SKUs.

How are SKUs typically structured?

There's no universal format, but effective SKUs are short, consistent, and human-readable. The structure matters less than the discipline: mixed conventions lead to duplicate entries, lookup failures, and inventory errors at scale.

How do SKUs affect inventory management?

SKUs are the atomic unit of inventory. Every stock count, reorder trigger, low-stock alert, and fulfillment action happens at the SKU level, not the product level. Without them, you know you have "t-shirts"; with them, you know you have 43 Blue Large and 2 Red Small, and can act accordingly.