Amazon FBA Barcodes: FNSKU vs UPC, and When to Use Which
A practical guide to Amazon FBA barcode requirements - what FNSKU and UPC are, how Amazon's 2026 policy change affects sellers, and how to decide which label goes on your products.
Since March 31, 2026, Amazon has required an FNSKU label on every FBA unit from a reseller, while a brand owner with the Brand Representative role in Brand Registry can ship with the manufacturer's UPC alone. The FNSKU (X00 plus seven characters) identifies the product and your seller account. The UPC identifies the product for every seller. The FNSKU label prints as a Code 128 barcode and the UPC prints as a UPC-A symbol, each with the number underneath, and the wrong one on the box leaves your inventory stranded at the fulfillment center.
FNSKU vs UPC at a glance
| FNSKU | UPC / GTIN | |
|---|---|---|
| Issued by | Amazon (free, automatic) | GS1 (paid registration) |
| Identifies | Product + specific seller account | Product globally, regardless of seller |
| Format | X00xxxxxxx (10 chars, Code 128) | 12 digits (UPC-A) or 13 digits (EAN-13) |
| Unique per seller? | Yes | No, shared by all sellers of the same product |
| Required after March 2026 | Mandatory for resellers | Permitted for brand owners with the Brand Representative role |
| Commingling risk | None (segregated inventory) | Eliminated after March 2026 |
What is an FNSKU?
FNSKU stands for Fulfillment Network Stock Keeping Unit. It is Amazon's own identifier, a barcode that encodes both a product and the specific seller account that owns it. It always starts with X00 and is 10 characters long, for example X001KR74B2. It is encoded as a Code 128 barcode.
You cannot buy an FNSKU or generate one externally. Amazon creates it when you set up FBA inventory in Seller Central and ties it to your account. Two sellers listing the same product have different FNSKUs for that product, because the code identifies the seller as well as the item. When a receiving associate scans an FNSKU, Amazon knows whose unit it is, which listing it belongs to, and which seller earns the sale. That is how a warehouse handling inventory from tens of thousands of sellers attributes each unit to one of them.
What is a UPC?
A UPC (Universal Product Code) is a 12-digit UPC-A barcode identifier issued through the GS1 standards system, and through GS1 US for North American brands. The 13-digit version used outside North America is called an EAN-13. Both are GTINs (Global Trade Item Numbers). A GTIN identifies a product globally and belongs to the brand, whichever retailer sells it.
The FNSKU is account-specific and the UPC is not. If twenty sellers all list the same product, they share one ASIN (Amazon's catalog identifier) and one UPC, but each has a unique FNSKU. That distinction between "identifies the product" and "identifies the product owned by this seller" is the root of every FNSKU vs UPC question.
Buy your UPC directly from GS1 US. Amazon cross-checks GTINs against the GS1 database and verifies that the registered brand name matches your seller account, so a cheap code bought from a third-party reseller and registered to someone else's company gets your listing suppressed. GS1 US sells a single GTIN for $30 (one-time, no renewal), which suits a brand with one to three products, or a GS1 Company Prefix from $250 with annual renewal, which gives you a prefix to self-assign product numbers across your catalog.
What was commingling and why did it end?
For years, Amazon let sellers choose between labeling every unit with an FNSKU (segregated inventory) and relying on the manufacturer's UPC so Amazon could pool their units with physically identical units from every other seller (commingled or stickerless inventory).
Commingling had one appeal, which was that no label had to be applied before shipping. In exchange, your buyer could receive a unit from a different seller's inventory, and if that seller's batch was counterfeit, damaged, or sourced from a different region, it shipped under your listing and your reviews took the hit. That made commingling a gift to counterfeiters, and a private label seller had no control over which units shipped under their brand.
Amazon announced the formal end of commingled inventory effective March 31, 2026. All units arriving at fulfillment centers after that date must be attributable to a specific seller. The commingling argument is over.
The 2026 rules
The requirement after March 31, 2026 depends on your role in Amazon Brand Registry.
Resellers without the Brand Representative role must put an FNSKU label on every unit. This covers retail arbitrage sellers, wholesale resellers, authorized distributors, and any seller enrolled in Brand Registry under a Reseller role. Even if the manufacturer's UPC is printed on the product, apply an FNSKU sticker before shipping to Amazon.
Brand owners with the Brand Representative role can ship with the manufacturer's printed barcode alone. Amazon attributes the inventory to your account by tracking it virtually, with no physical pooling, so your units stay yours. The exception is a UPC that maps to more than one ASIN. Those units need FNSKUs.
Amazon also discontinued its FBA prep and labeling service in the US on January 1, 2026, so Amazon no longer applies labels at the fulfillment center. Finish all labeling before you create the shipment, because unlabeled units arriving after that date are rejected with no on-site correction. Third-party prep centers charge about $0.10-$0.55 per unit for labeling alone, or $0.75-$1.50 for full prep, if you cannot label at source.
How to get your FNSKU
FNSKUs are free and generated automatically through Seller Central.
- Log into Seller Central. Go to Settings > Fulfillment by Amazon > FBA Product Barcode Preference. Set the default to "Amazon Barcode" (FNSKU).
- Go to Inventory > Manage FBA Inventory. Add the FNSKU column to your view. The X00 code appears once the listing is active in FBA.
- To print labels, select the product and choose "Print item labels" from the action dropdown. Pick your label format (30-up Avery-compatible sheet for desktop printers, or thermal roll format), specify the quantity, download the PDF, and print.
Each product variation (size, color, configuration) has its own FNSKU, because each is a distinct ASIN and a distinct listing in Amazon's catalog. Generate and print labels separately for each variant.
Label placement and print quality
Amazon enforces these label rules at receiving.
- The label must be at least 1 inch by 2 inches. Amazon's default PDF format generates 30-up Avery-compatible labels at roughly 1 by 2 5/8 inches.
- Put it on a flat surface on the outermost layer of the sellable unit. Keep it off curves, corners, seams, and textured surfaces, because bar spacing distorts on a curve and the scan fails. A polybagged unit gets its label on the outside of the polybag, on a flat face.
- If you use an FNSKU, cover every other scannable barcode on the unit. A visible UPC beside an FNSKU means Amazon may scan the wrong code.
- Print black on a white, non-reflective background at 300 DPI or higher. Direct thermal printers (Zebra, Dymo, Rollo) are the usual choice, because they use no ink and print the same label every time. Test-scan a label from every new batch before you commit to a full print run.
- The label carries the Code 128 barcode, the FNSKU in human-readable text below it, the product description, and the condition ("New").
Mistakes that cost sellers money
Labeling only the outer case. Amazon scans individual units at receiving, so every unit inside a case pack needs its own label. Miss one and those units are unsellable until corrected.
Wrong FNSKU on a size variant. A Large FNSKU on a Medium unit creates an inventory attribution error that is slow and painful to resolve. For multi-variant products, generate labels per variant, give each print file the variant name, and check it before batch printing.
Barcode on a curved surface. Any flex or curve distorts bar spacing and the label fails at receiving. Cylindrical containers get their label on a flat side panel, full stop.
The bottom line
If you are a private label brand owner with the Brand Representative role in Brand Registry, the 2026 change works in your favor. Print your GS1-registered UPC on your packaging at the factory and skip the label step. Your per-unit cost drops and your supply chain gets simpler. If you are a reseller, whether retail arbitrage, wholesale, or authorized distributor, the FNSKU is now mandatory on every unit. Apply it at the supplier, at a prep center, or yourself before shipping, and build the cost into your margins.