FNSKU stands for Fulfillment Network Stock Keeping Unit. It’s an Amazon-specific barcode that links a physical product in an Amazon warehouse directly to you, the seller. When a warehouse worker scans an FNSKU label, Amazon knows exactly whose inventory that unit belongs to and credits the sale accordingly. If you sell through Fulfillment by Amazon (FBA), understanding how FNSKUs work is essential for protecting your inventory and your reputation.
How FNSKU Differs From Other Amazon Codes
Amazon’s ecosystem uses several overlapping identification systems, and it’s easy to confuse them. Here’s how they break down.
A UPC (Universal Product Code) is the standard 12-digit barcode you see on products in any retail store. It identifies the product itself, not who’s selling it. You typically need a UPC when first creating a product listing on Amazon.
An ASIN (Amazon Standard Identification Number) is a 10-character alphanumeric code Amazon assigns when a product enters its catalog. You don’t create it directly. Instead, you provide a product identifier like a UPC when listing your item, and Amazon either assigns a new ASIN or connects your listing to an existing one. The ASIN lives in Amazon’s system and isn’t something you print on packaging.
The FNSKU goes a step further. It’s a barcode you physically apply to each unit before shipping it to Amazon’s warehouse. Unlike a UPC, which only identifies the product, an FNSKU ties that specific unit to your seller account. If five different sellers offer the same product, each seller’s inventory gets a unique FNSKU. That distinction matters more than it might seem.
Why FNSKUs Exist: The Commingling Problem
When sellers ship products to Amazon using only the manufacturer barcode (the UPC), Amazon may “commingle” that inventory. Commingled units are tracked virtually using the manufacturer barcode, meaning all identical products from different sellers across the country become interchangeable. If a customer orders your product, Amazon might ship a unit that was actually sent in by a completely different seller.
This creates a real risk. If another seller sends in counterfeit or damaged units of the same product, those items could end up going to your customers under your name. You’d get the negative review, the return, or the potential policy violation even though the defective unit was never yours.
Items with FNSKU stickers are segregated by Amazon. When someone places an order, it gets fulfilled specifically from your available FBA inventory. The sale is credited to you, and only your actual units go out the door. For sellers who care about quality control, using FNSKUs is the straightforward way to keep your inventory separate from everyone else’s.
How to Get an FNSKU for Your Product
You don’t apply for an FNSKU separately. Amazon generates one automatically when you set up a product listing and enroll it in FBA. In your Seller Central account, you can configure your barcode preference to use Amazon barcodes instead of manufacturer barcodes. Once that’s set, Amazon assigns a unique FNSKU to your listing.
To print your FNSKU labels, you have two options in Seller Central:
- Through the Send to Amazon workflow: When preparing a shipment, click “Print SKU labels” in the information column next to your product. You can also print all unit labels for an entire shipment at once at the end of step one.
- Through Manage Inventory: Select the products you want labels for, then choose “Print item labels” from the action dropdown menu.
The labels Amazon generates include the FNSKU barcode, the product title, and the condition. You print them, stick one on each unit (covering any existing manufacturer barcode so warehouse scanners don’t read the wrong code), and ship them off.
Labeling: Do It Yourself or Pay Amazon
You can apply FNSKU labels yourself before shipping inventory to Amazon, or you can use Amazon’s FBA Label Service and let warehouse workers handle it. The Label Service costs $0.55 per unit. For small shipments, that fee adds up quickly, so many sellers invest in a thermal label printer and handle it in-house. For large or time-sensitive shipments, paying Amazon to do it can save a logistical headache.
Every item sent to an Amazon fulfillment center needs a barcode for tracking. If your product isn’t eligible to use a manufacturer barcode, Amazon requires an FNSKU label. Even if your product is eligible for manufacturer barcodes, choosing FNSKU labels gives you the inventory segregation benefit described above.
Upcoming Rule Change for Resellers
Starting March 31, 2026, Amazon’s barcode requirements are shifting. Brand owners will still be able to use manufacturer barcodes without stickers. However, resellers will be required to use Amazon barcodes (FNSKUs) on their products, even if those products already have a manufacturer barcode. If you’re a reseller who has been relying on commingled inventory, this change means you’ll need to start labeling every unit with an FNSKU before sending it in.
For private label sellers who already use FNSKUs, nothing changes. For resellers, this is worth planning for now, since it affects your prep workflow, your per-unit costs, and potentially your choice of prep service or labeling setup.
When You Need an FNSKU and When You Don’t
If you sell through FBA and want your inventory tracked separately, you need FNSKUs. If you fulfill orders yourself (Fulfilled by Merchant), FNSKUs don’t apply since the product never enters Amazon’s warehouse. Similarly, if you’re a brand owner selling a unique product that no other seller lists, the risk of commingling is lower, and you may be comfortable using your manufacturer barcode. But even in that scenario, FNSKU labeling provides an extra layer of certainty that Amazon is pulling from your inventory and crediting sales to you correctly.
For most FBA sellers, especially those selling products that other sellers also offer, FNSKU labeling is the simplest way to protect your business from inventory mix-ups and the customer complaints that follow.