SKU vs UPC vs FNSKU at a glance
| SKU | UPC | FNSKU | |
|---|---|---|---|
| Who creates it | You (the seller) | GS1 (licensed to the brand) | Amazon |
| Format | Alphanumeric, any length you choose | 12-digit numeric barcode | Amazon code starting with X0 or B0 |
| Scope | Internal to one business | Universal across retailers | Inside Amazon fulfillment centers |
| Purpose | Inventory tracking and picking | Product identification at checkout | Ties a unit to a specific FBA seller |
What is a SKU?
A SKU (stock keeping unit) is the code you invent to track a sellable item in your own systems. Good SKUs encode meaning, for example HOOD-BLK-M for a black hoodie in medium. Every variant gets its own SKU, which is what a warehouse actually picks against. Well-structured SKUs are the backbone of accurate inventory management.
What is a UPC?
A UPC (universal product code) is the familiar 12-digit barcode scanned at retail checkout. UPCs are licensed through GS1, the global standards body, so a given product carries the same UPC no matter who sells it. The number under the bars is the GTIN-12. If you plan to sell into retail or on major marketplaces, budget for GS1-licensed UPCs per variant.
Where the FNSKU fits in
Amazon adds a third identifier: the FNSKU, its internal code that maps a physical unit to a specific seller inside FBA. Most FBA shipments need an FNSKU label applied so units scan correctly at Amazon receiving. Applying FNSKU labels correctly (and covering the existing barcode when required) is a standard part of Amazon FBA prep.
When you need each one
- Selling only on your own site: SKUs are enough.
- Selling on marketplaces or into retail: SKUs for your operations plus GS1-licensed UPCs for the products.
- Selling via Amazon FBA: all of the above plus FNSKU labels on the units you send in.
A 3PL keeps these identifiers straight for you: RitePrep picks against your SKUs, ships retail orders with the right UPC-labeled cartons, and preps FNSKU labels for FBA, all from one Austin warehouse.