FNSKU

What an FNSKU does

Every unit sent to an Amazon fulfillment center needs a barcode Amazon can track. Per Amazon's barcode requirements, that's either a manufacturer barcode (UPC, EAN, JAN or ISBN) or an Amazon barcode, which is the FNSKU label. A manufacturer barcode says what the product is. An FNSKU says whose unit it is, so Amazon can track your inventory separately from other sellers' stock of the same product.

One FNSKU covers every unit of your listing. You print the same label for each unit; it isn't a per-item serial number. Amazon assigns it, and in its seller APIs it sits next to the ASIN and seller SKU as Amazon's fulfillment network SKU identifier.

How it differs from an ASIN, UPC and SKU

• ASIN: Amazon's ID for the product in its catalog. Every seller of that product lists against the same ASIN, and reviews and ratings belong to it.
• UPC or EAN: the manufacturer's retail barcode, licensed from GS1. It's the same on every unit of the product wherever it's sold. See SKU vs UPC.
• SKU: your own code for the item, used in your store, your warehouse and as the seller SKU in Seller Central. See SKU.
• FNSKU: Amazon's code for your offer of that product inside its fulfillment network. To switch an ASIN to Amazon barcodes, Amazon has you create a new seller SKU on it; the ASIN's reviews stay put.

Who needs FNSKU labels

Since March 31, 2026, the answer depends on whether you own the brand. That's when Amazon ended commingling, the practice of filling an order from any seller's matching unit. Customers who buy from you now get units from your inventory only, returns and removals included.

• Brand owners enrolled in Brand Registry as the brand representative can keep sending eligible products on their manufacturer barcode, with no sticker. Enrolling the brand isn't enough on its own; the products have to be registered to it.
• Resellers, including authorized resellers, must put an FNSKU label on every unit they send in, even when the product has a UPC. Units that arrive without one are treated as defective, and units that aren't labeled to Amazon's rules aren't eligible for reimbursement.
• Products with no manufacturer barcode need FNSKU labels whoever sends them, including brand owners whose products have a GTIN exemption.

What the label has to carry

Amazon's label rules ask for the FNSKU barcode, the product name and the item condition, with 0.25 inch of white space on the sides and 0.125 inch at the top and bottom. Labels are black ink on white, non-reflective stock with removable adhesive, between 1 × 2 inches and 2 × 3 inches. Print on a thermal or laser printer, not inkjet; Amazon recommends 300 dpi or better, and the label has to stay scannable for 24 months.

The label covers every other visible barcode on the unit except serial-number and Transparency codes. Keep it off curves and corners, and label each unit inside a case pack, not just the case.

Printing and applying FNSKU labels

Seller Central prints FNSKU labels from Print SKU labels in Send to Amazon or Print item labels in Manage Inventory, either in a thermal format or as a PDF for laser sheets such as the 30-up US letter sheet. Our free barcode maker makes FNSKU labels from a list of codes, as Code 128 barcodes with the title and condition line, at 2.25 × 1.25, 3 × 1 or Avery 5160 sizes. If you have Amazon's 30-up PDF and a thermal printer, the label resizer splits the sheet into single 2.25 × 1.25 labels.

Amazon stopped offering item labeling for FBA shipments to its U.S. store on January 1, 2026, so the labels go on before inventory ships, either by you or by a prep center.