SKU (Stock Keeping Unit)

What Is a SKU?

A SKU, or stock keeping unit, is an internal identifier that represents one specific sellable item. Every variation that needs to be counted separately gets its own SKU, so a t-shirt sold in three colors and four sizes typically has twelve SKUs.

SKUs are different from UPCs or other barcodes printed by manufacturers. A UPC is a universal code shared across retailers, while a SKU is defined by the brand or warehouse and can follow whatever logic makes the catalog easy to manage.

How It Works

A good SKU is short, unique and readable. Many brands build the code from meaningful segments, such as product line, style, color and size. For example, TEE-CLS-BLK-M could stand for a classic tee in black, size medium.

Once a SKU exists, it becomes the key that connects the store, the warehouse management system and the accounting records. Orders reference SKUs, inventory counts are kept by SKU, and pickers scan the barcode tied to a SKU to confirm they grabbed the right unit.

• Use letters and numbers only, and avoid characters that look alike, such as O and 0.
• Keep the format consistent across the whole catalog.
• Never reuse a retired SKU for a new product.

Why It Matters for Ecommerce Brands

Clean SKUs are the foundation of accurate fulfillment. When two variants share a code, or one product has several codes, inventory counts drift and the wrong item ships. Clear SKUs also make reporting simple, because sales velocity, reorder timing and storage needs can be tracked for each variant.

Before onboarding with a 3PL, it pays to audit your catalog, remove duplicates, retire discontinued codes and make sure every physical item has a barcode that maps to exactly one SKU.