FNSKU labels for Amazon resellers: when you need one and how to apply it

What an FNSKU is, and how it differs from a UPC, SKU and ASIN

FNSKU stands for Fulfillment Network Stock Keeping Unit. It's the barcode Amazon creates for your offer of a product when you sell it through Fulfillment by Amazon (FBA), so the warehouse knows which units are yours.

An Amazon staff member put it simply in a Seller Forums post about SKUs and FNSKUs: an FNSKU works like a manufacturer's barcode, but it's tied to your inventory in Amazon's fulfillment network. It belongs to one seller, no two sellers share one, and an Amazon barcode FNSKU starts with an X. That last detail is a handy way to tell it apart from a UPC on a label.

You'll meet four identifiers when you buy wholesale and sell on Amazon. They do different jobs:

A simple way to hold it in your head: the UPC and the ASIN describe the product. The SKU and the FNSKU describe your stock of it. Ten sellers can sell the same UPC on the same ASIN, and each of them has a different FNSKU.

The UPC is still useful to you. It's how you match a supplier's price list to Amazon listings, which our price list guide walks through step by step. It just isn't the barcode Amazon goes by when a reseller's units arrive anymore.

FNSKU vs UPC: which one goes on the unit

If you resell a brand you don't own and send it to FBA, the FNSKU goes on the unit and covers the UPC. The next section explains why.

If you ship every order yourself, your units never go into Amazon's warehouses, so you don't need an FNSKU at all.

What changed when commingling ended

Commingling was Amazon filling an order with an identical unit from whichever stock was closest in its network, even when that stock belonged to another seller. It let Amazon ship from the nearest warehouse. For resellers it also meant a unit from someone else's stock could ship on your order, with your name on the sale.

Amazon announced on its US Seller Forums that commingling would end for inventory shipped on or after March 31, 2026, and changed who may ship products under the manufacturer barcode.

Three things in that rule trip resellers up.

Authorized resellers are included. Brand Registry has two selling roles. Amazon's guide to Brand Registry roles describes Brand Representative as the role for sellers employed by the brand, and Reseller as the role for outside sellers the brand authorizes. The commingling announcement names Brand Representative only. So a letter of authorization, or the Reseller role, doesn't let you skip the label. Our letter of authorization guide covers what those do get you.

Amazon won't put the label on for you. Amazon stopped offering prep and item labeling in the US marketplace on January 1, 2026. Its Selling Partner API notice says "AMAZON" is no longer accepted as the prep owner or the label owner. Put the two changes together and every unit a reseller sends needs a label applied by someone outside Amazon.

Older offers may still be set up the old way. Your FBA barcode preference decides whether a new FBA listing uses the manufacturer barcode or an Amazon barcode. In the forum post on SKUs and FNSKUs, written before this change, an Amazon staff member explained that the preference has to be set before the FBA listing is created. If you created offers under the manufacturer barcode before the change, check how each one is set up before you build its next shipment. Our log of Amazon rule changes covers what Amazon's barcode FAQ says about moving those SKUs.

We could not open Amazon's Seller Central help pages on barcodes, because they need a sign-in, so the details on this page come from Amazon's public announcement and its sell.amazon.com guides. If you're signed in, Amazon's barcode choice and labeling FAQ is the page to read next.

Do you need an FNSKU? A decision tree

Work down the questions and stop at the first answer that tells you what to do.

A note on question 3. Amazon's prep and labeling guide lists kinds of products that need Amazon barcodes whatever the seller's role, such as used items, media, restricted or dangerous goods, and consumable or topical products. It adds that brand-registered sellers may be eligible for an exemption to use manufacturer barcodes on some of them. That is a question for brand owners. For a reseller sending new products into FBA, nearly every path ends in the same place: an FNSKU label on every unit.

Label size, placement and printers

Amazon's FBA prep, packaging, and labeling guide on sell.amazon.com sets out the label rules in plain words. Here they are, with what they mean at your packing table.

What the label shows. A scannable barcode, the FNSKU number, the product title and the condition (new or used). Seller Central lays all of that out for you when you print, so you never design a label yourself.

Size. 1 to 2 inches tall and 2 to 3 inches wide. Two common stock sizes fit inside that range: the 30-per-sheet letter labels (1 x 2-5/8 inch) for laser printers, and 1.25 x 2.25 inch rolls for thermal printers.

Paper and printer. Black ink on non-reflective paper with an adhesive backing. Amazon recommends a laser printer at 300 DPI. A thermal label printer is the common alternative: it prints one label at a time from a roll, which suits labeling as you pack, and label printer makers publish guides for printing Amazon's labels on theirs.

Placement. Put the label on a smooth, flat surface, away from corners, edges and curves, so it lies flat and scans. If the product goes in without extra packaging, the label covers the original barcode (UPC, EAN or ISBN) so that one can't be scanned by mistake. If you bag or box the product, the label goes on the outside, readable without opening anything.

What Amazon won't accept. Damaged or photocopied labels. And a Transparency code must never be covered by another label, or cover one itself.

The carton too. Remove, cover or cross out any old barcodes on the outside of shipping boxes you reuse, with opaque tape or a black marker, so the warehouse scans only your box label.

What happens otherwise. Amazon's guide says it may refuse, return or repackage inventory that doesn't follow its prep rules, at your expense.

Printing labels in Seller Central

Your FNSKU shows next to each FBA offer in your inventory list, and you print labels in Seller Central, including while you build a shipment in Send to Amazon. You pick the label format and size before printing, so match it to the stock in your printer. We haven't captured these screens for this guide yet, and Amazon's help page on printing needs a sign-in, so check the options in your own account.

Who labels: you, your prep center or your supplier

With Amazon out of the picture in the US, one of three people puts the label on.

Doing it yourself. You need a printer, label stock, poly bags where a product needs them, and a table. It's a sensible way to handle your first orders while you learn what each product needs, and our first wholesale order guide covers how big those orders should be.

Using a prep center. Prep centers usually price labeling into their standard per-unit prep. Send written instructions for each SKU: the label file, whether the unit needs a bag, and anything special such as expiry dates. Our prep center guide covers choosing one and the questions to ask before you send anything.

From Stef's lesson (Restocking, 9:20 to 9:37): when a prep center quotes its turnaround, he plans for more. "If your prep center says two days, maybe add three." Labeling is now part of every reorder's lead time, so give it room.

If your prep center works in Apex, Apex Red keeps your shipments, prep center messages and prep bills in one place, next to the rest of your Apex data. Red is in beta and opened by invitation. When your prep center is approved on Apex, it is free for you. See how Red works, or send your prep center to Apex.

Asking your supplier. Some distributors and brands will apply your FNSKU labels before they ship, sometimes for a fee. Ask before your first order: our distributor email templates give you a first email to adapt, and one line asking whether they label units for Amazon sellers is enough. If they agree, send the label file and say which barcode the label must cover. Then check the first carton yourself, or have your prep center check it, because a wrong label becomes your problem once it reaches Amazon's warehouse.

What labeling adds to your cost per unit

The label itself costs cents. The work around it, and the prep that usually comes with it, is what shows up in your numbers.

So the cheap-looking option isn't always the cheap one. By those estimates, a small seller labeling at home pays about what a prep center charges once their own time counts. Ask any prep center for an itemized quote, so you can see what's inside its per-unit rate and compare like with like. Our prep center guide covers the other charges that show up on a prep invoice.

A dollar a unit sounds small. Whether it is depends on what the unit cost you. Here is one example, using $1.00 for prep and labeling, which sits inside the reported range for a smaller seller:

Say the $4.00 product leaves you $2.00 profit after Amazon's fees, before prep. A $1.00 prep and label charge cuts that profit in half. Cheap, fast-moving products are where labeling decides whether a deal still works.

That's why it belongs in your landed cost: what you pay the supplier, plus freight to your prep center, plus prep and labels, plus shipping to Amazon, plus the inbound placement fee if your shipment pays one. Our Amazon FBA fees guide covers the fees Amazon takes when the unit sells, and the startup cost guide budgets for prep from your first order.

Try it with your own numbers. The calculator below has a field for prep and shipping to Amazon per unit. Put your labeling cost there and watch the return on investment move. For a version you can bookmark, there's the free profit calculator. It counts the FBA fee as part of your cost when it works out return on investment, so its ROI reads a little lower than this one.

In Apex, you enter your inbound shipping and prep costs, and Apex Blue counts them in each purchase order's landed cost, projected profit and ROI. See how Blue works.

Transparency codes

Transparency is Amazon's product serialization and anti-counterfeiting program for brands. Amazon's Transparency page explains that an enrolled brand assigns a unique code to every unit of an enrolled product, and that codes are scanned when units arrive at an Amazon fulfillment center. Enrolled products can't be listed in the stores Transparency covers without valid codes, and shoppers can scan a code with the Amazon Shopping app or the Transparency app to check it.

Transparency codes carry a "T" logo, and they differ from an FNSKU in two ways. A Transparency code is unique to each unit, while your FNSKU is the same on every unit of your offer. And Transparency codes come only from the brand, while Amazon gives you your FNSKU.

What that means when you resell an enrolled brand:

• You still need your FNSKU. Amazon's commingling announcement makes no exception for Transparency products, and its labeling guide says a Transparency code must not cover, or be covered by, any other label. So expect a reseller's unit to carry both: your FNSKU and the brand's Transparency code, side by side.
• The code comes from the brand. Amazon's page describes brands applying codes themselves or through service providers and co-packers. A reseller can't create them.
• Ask before you buy. If a product is enrolled, ask your supplier whether units arrive with codes on. Amazon checks the codes when units arrive, and its reports for brands count units blocked from shipment because a code was missing or invalid.
• Don't cover it. Put your FNSKU label beside the Transparency code, never over it.

Labeling is one part of stage 7, prep and ship, on the Amazon wholesale roadmap. The next step is getting the boxes to Amazon, which starts with how your shipment is split.