Amazon sellers deal with two kinds of barcodes, and mixing them up causes listing errors and FBA problems. A UPC identifies the product itself, worldwide. An FNSKU is Amazon’s own barcode that identifies your units of that product in Amazon’s warehouses. Here is what each one does and when you need it.
Quick answer
You need a UPC (or another GTIN, or a GTIN exemption) to create a product listing. If you use FBA, you usually also label each unit with an FNSKU, unless your product is eligible to use the manufacturer barcode.
What a UPC is
A UPC is a 12-digit product barcode, part of the GTIN family that also includes EAN codes. It identifies a product across all retailers. Amazon checks UPCs against the GS1 database, so buy them from GS1 rather than from cheap resellers, or your listings can be removed.
What an FNSKU is
An FNSKU is the Fulfillment Network Stock Keeping Unit that Amazon assigns to each product you send to FBA. It usually starts with X00 for products with a UPC. You print it from Seller Central and put it on each unit, so Amazon knows the unit belongs to you.
Why the FNSKU matters
- It keeps your units separate from other sellers’ units of the same product.
- It traces customer complaints and returns back to your inventory.
- It protects you if another seller sends in counterfeit or damaged units of the same product.
Manufacturer barcode instead of FNSKU
Some products can be tracked with the manufacturer’s barcode, so you don’t need to apply an Amazon label. Seller Central shows whether a product is eligible. Brand owners often choose FNSKU labels anyway, for full traceability.
Getting it right
- Buy UPCs from GS1 under your company name.
- Print FNSKU labels from Seller Central and cover any other barcodes on the unit.
- Use the right label size and a printer that produces sharp barcodes.
- Check one unit by scanning it before you label a whole shipment.
Next step: how to label your FBA boxes.
Questions sellers ask
Can I use one UPC for different sizes or colors?
No. Each variation needs its own UPC and gets its own FNSKU.
Do I need a UPC to sell on Amazon?
Usually, yes. Some products qualify for a GTIN exemption, for example private-label items without barcodes, which you request in Seller Central.
Sources: Amazon Seller Central help on product IDs and FBA labeling, and GS1 US, checked November 2026.