How to Generate FNSKU Barcodes for Amazon FBA (Step-by-Step Guide)

If you're shipping inventory into Amazon's fulfillment network, at some point you'll run into a requirement your UPC code doesn't satisfy on its own: Amazon usually wants its own barcode, called an FNSKU, on every unit. Here's what it actually is and how to get it right the first time, since labeling mistakes are one of the more common reasons FBA shipments get flagged or delayed.

What an FNSKU actually is

FNSKU stands for Fulfillment Network Stock Keeping Unit. It's a unique identifier Amazon generates for each product listing you enroll in FBA, and it exists for a specific reason: your UPC identifies your product in general, but it doesn't tell Amazon's fulfillment system which specific listing — yours — a unit belongs to. If another seller lists the same product under their own account, Amazon needs a way to tell your inventory apart from theirs inside the same warehouse. The FNSKU is that separator.

FNSKU vs UPC — why you need both

Your UPC stays the same no matter who's selling the product. Your FNSKU is tied specifically to your seller account and that one listing. If you're using Amazon's standard Fulfilled by Amazon service without opting into their manufacturer barcode exemption, Amazon will generally require the FNSKU barcode on the unit instead of, or in addition to, the manufacturer's original UPC, precisely so inventory doesn't get commingled with another seller's stock of the same product.

Where your FNSKU comes from

Once you enroll a product in FBA and create a shipping plan, Amazon's Seller Central generates the FNSKU automatically for that listing. You don't design or choose the number yourself. What you're responsible for is turning that assigned code into a properly formatted, scannable barcode label and applying it correctly before the shipment leaves your hands.

Step-by-step: generating and printing the label

1. Locate the FNSKU for the listing inside your FBA shipping plan in Seller Central. It's tied to the specific SKU you're shipping, not your account as a whole.
2. Generate the barcode in Code 128 format, which is what Amazon's system expects for FNSKU labels. Our barcode generator supports Code 128 out of the box.
3. Check the print size against Amazon's minimum label size requirements before printing. A label that's technically readable on screen can still be rejected at a fulfillment center if it doesn't meet Amazon's physical sizing rules.
4. Print on a label that survives handling. Thermal labels hold up far better through the warehouse shipping and receiving process than inkjet-printed paper labels, which can smudge or peel.
5. Apply the label over or next to the original manufacturer barcode, following Amazon's current placement requirements, so a warehouse scanner reads your FNSKU rather than accidentally scanning the underlying UPC.

Mistakes that get FBA shipments rejected

• Covering the FNSKU with tape or a shipping label, which blocks the scan entirely at receiving.
• Printing at too small a size to save on label stock — the same core issue that causes any barcode to fail intermittently, and it's especially costly here because it can hold up an entire shipment, not just one unit.
• Reusing an old FNSKU label on a different batch after relisting a product. Amazon can generate a new FNSKU if a listing changes, and shipping product with a stale barcode causes mismatches at the warehouse.
• Applying the label over a curved or seamed part of the packaging, which distorts the barcode enough to cause read failures during receiving — the same issue that affects any barcode on a non-flat surface.

Generating labels in bulk

If you're shipping more than a handful of SKUs at once, generating FNSKU labels one at a time is a good way to introduce a mismatch between a barcode and its product. Look for a bulk-generation option that lets you input a full list of FNSKUs at once and export every label together, ideally with each barcode named or ordered to match your packing list, so there's no manual matching step where an error can slip in. Our bulk barcode generator is built for exactly this.

Should you just pay Amazon to label it instead?

Amazon offers an FBA Label Service that applies FNSKU labels on your behalf for a small per-unit fee, which is worth considering if you're shipping a small batch and want to avoid the labeling step entirely. For sellers moving larger volumes regularly, generating and applying labels yourself is almost always cheaper once you factor in Amazon's per-unit charge across hundreds or thousands of units, and it gives you more control over label quality and placement rather than relying on Amazon's warehouse staff to apply it correctly. The right call usually comes down to shipment size and how much your time is worth against the per-label fee.

Quick answers

Can I use my product's regular UPC instead of an FNSKU? Only if you've opted into Amazon's manufacturer barcode exemption for that listing. By default, FBA expects the FNSKU.

Does the FNSKU change if I update my listing? It can, particularly if you create a new listing rather than editing an existing one. Always pull the current FNSKU from your active shipping plan rather than reusing an old label.

What barcode format does Amazon require for FNSKU labels? Code 128 is the standard format Amazon's systems expect for FNSKU labels.