SKU: your own internal code
A SKU is a code you define yourself, structured however makes sense for your business (for example, including a category prefix, size, or color code). It is not standardized, not shared with other businesses, and does not need to be globally unique — only unique within your own catalog.
Because you control the format, a SKU can encode information a barcode can't (like "TSH-BLU-L" for a blue large t-shirt), which makes it useful for internal organization even though it means nothing to an external system.
UPC and EAN: standardized retail barcodes
A UPC is a 12-digit standardized barcode, issued through GS1, primarily used in the United States and Canada. An EAN (technically GTIN-13 today, though "EAN" is still the common term) is the 13-digit equivalent used primarily in Europe and the rest of the world. Both identify a specific product the same way across any retailer or system that reads it, which is what makes them work at a point-of-sale register or in a marketplace listing.
You typically need one or the other depending on where you sell, not both for the same product a UPC-only product sold in the US and a EAN-only product sold in the EU are both normal; you don't need to assign a product both codes unless you are actually selling in both regions through channels that specifically require each format.
- SKU: internal, self-defined, unique only within your own catalog
- UPC: 12-digit standardized barcode, primarily North America
- EAN/GTIN-13: 13-digit standardized barcode, primarily outside North America
Using a SKU and a barcode together
Most inventory systems, including StockFlow, let you record both a SKU and a barcode (UPC/EAN/or other formats) on the same product. The SKU is what your team uses internally to find and organize products; the barcode is what gets scanned at receiving, at a register, or on a marketplace listing. They serve different audiences the SKU is for you, the barcode is for external systems and scanning hardware.
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