Three numbers, three jobs
| Code | Issued by | What it identifies | Example |
|---|---|---|---|
| UPC or EAN barcode (GTIN) | GS1 | The product across retail systems | 0036000291452 |
| ASIN | Amazon | The product page on Amazon | B0XXXXXXXX |
| FNSKU | Amazon | Your stock of that product in Amazon's warehouses | X001ABC2DE |
If several sellers offer the same product, they share one ASIN and usually one GTIN. Each reseller's units carry that seller's own FNSKU, which is how Amazon knows whose unit it is picking when an order comes in.
Who needs FNSKU labels
Amazon warehouses scan units when they arrive and when they are picked, so each unit has to identify both the product and the seller. On March 31, 2026, Amazon ended inventory commingling in its US store. Before that, units of the same product from different sellers could be pooled under the manufacturer barcode. The rules since then, in short:
- Resellers (selling another company's brand) must put an FNSKU label on every unit they send to FBA, even if the product already has a UPC or EAN.
- Brand representatives in Amazon Brand Registry can use the manufacturer barcode for eligible products without an additional FNSKU label.
- Anyone unsure should use FNSKU labels, which are open to every seller, after confirming the product's barcode setting.
Barcode requirements can differ among Amazon stores. Follow the setting shown for each product in Seller Central.
How to print FNSKU labels
The simplest route is Amazon's own label printing. In Seller Central, open your inventory or shipment, choose to print item labels, pick the label format that matches your sheets or thermal printer, and print. Amazon generates the Code 128 barcode together with the product title and condition, which is exactly what the warehouse expects.
- Label size: Amazon's guidance calls for labels between about 1 × 2 inches and 2 × 3 inches. Common choices are 30-up letter sheets or 2.25 × 1.25-inch thermal labels.
- Printer: a thermal printer at 203 or 300 dpi, or a laser printer. Inkjet labels can smudge.
- Placement: on a flat surface of the unit, not over an edge or a seam.
- Cover other barcodes. The FNSKU should be the only scannable barcode on the outside of the unit. Place the label over the UPC or EAN, or cover it separately.
Always check Amazon's current FBA product label requirements page in Seller Central before a large shipment. Rules for label sizes, polybags, and prep can change, and Amazon may relabel noncompliant units at your expense.
When to generate an FNSKU barcode yourself
Amazon's labels cover most needs. Generating the barcode yourself makes sense when:
- You print it directly on the packaging. Printing the FNSKU barcode on a box eliminates the need to apply a separate FNSKU sticker to each unit. The barcode has to meet the same size and scan requirements as a label, and still be the only scannable code outside.
- A prep center or factory needs artwork. Some suppliers want a vector file to add to their own label layout.
- You bundle several products. A physical multipack or bundle needs a listing for the packaged item, and barcodes for the individual items must not be scannable through the outer packaging.
In the Barcode Pro studio, choose Code 128, type the FNSKU exactly as Seller Central shows it (uppercase, no spaces), and check that the scan badge reads back the same value. Keep bars at about 0.25 mm or wider as a starting point, leave the quiet zones clear, and scan a printed proof at the final size. Export an SVG for print artwork, or a PNG at 300 dpi or more for label software. Add the product title and condition as text if you are building your own label, because Amazon's labels include them.
Common FNSKU mistakes
- Using the ASIN instead of the FNSKU. For most sellers they differ. Copy the value labeled FNSKU.
- Leaving the UPC or EAN visible. A warehouse scanner may read the wrong code first.
- Tiny or truncated labels that fail to scan through a polybag.
- Mixing up variants. Each separately listed size and color needs the correct identifier for that variation. Label them in separate batches.
- Styling the barcode. Warehouse scanners work fastest with plain black-on-white. Save the design ideas for the rest of the pack.
Your listing may still need a GTIN
An FNSKU does not replace the product's UPC or EAN. Resellers list against the brand's existing GTIN; brand owners need their own. To create a new listing, Amazon generally requires a product identifier and may verify GTINs against GS1 records, unless the product qualifies for a GTIN exemption. If you are just starting out, read how to get a barcode for your product first.
Frequently asked questions
What is an FNSKU?
Fulfillment Network Stock Keeping Unit: an identifier Amazon assigns to your FBA inventory for a particular product. It links a physical unit in the warehouse to your seller account and listing. Most start with X0. In the US store, resellers have had to label every FBA unit with their FNSKU since March 31, 2026.
Is the FNSKU the same as my UPC or EAN?
No. Your UPC or EAN barcode carries a GTIN that identifies the product across retail systems. The FNSKU is Amazon's own code that identifies your stock of that product inside Amazon's warehouses. Amazon generally requires a product identifier to create a listing unless an exemption applies.
What barcode type is an FNSKU label?
Amazon generates FNSKU labels with Code 128 barcodes, with the FNSKU, the product title and the condition printed as text on the label.
Can I print the FNSKU on my packaging?
Amazon allows the FNSKU barcode to be part of your packaging as long as it meets its label requirements for size, scannability and placement, and is the only barcode that can be scanned on the outside. Check Amazon's current FBA labeling rules before a print run.