Glossary
A unique code (stock keeping unit) assigned to every product variant sold or stored, used to track quantities, locations and sales item by item.
A SKU (stock keeping unit) is the internal identifier of one specific item: not "office chair", but "office chair, Ergo model, black, with armrests". Every combination that is stocked, sold or counted separately gets its own SKU. It is the key on which inventory, orders, sales reports and the WMS rely.
The SKU is defined by the company for its own needs. The UPC (or EAN) is the universal code printed by the manufacturer, shared by every retailer. A SKU can be linked to a UPC, but the company remains free to structure it its own way. The barcode is merely the printed representation of either one.
A good SKU is short (8 to 12 characters), unique and readable by a human: segments that indicate the category, the model and the attributes, such as CHA-ERGO-BK-AR. Avoid ambiguous characters (O and 0, I and 1), never reuse a retired SKU and do not encode information that changes (price, supplier). A SKU that carries variable data becomes wrong the day that data changes.
Without a unique identifier, the same product shows up under three descriptions, the physical count never matches the system and purchase orders duplicate references already in stock. Creating a SKU nomenclature is often the first task of a WMS or ERP implementation.
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The SKU is the item's internal code; the barcode is its printed representation, readable by a scanner. A barcode can encode a SKU or a UPC.
Yes, if they are stocked or sold separately. A t-shirt in 4 sizes and 3 colours represents 12 SKUs.
Between 8 and 12 in general. Enough to be unique and descriptive, short enough to be read and typed without error.
