Amazon's Two Barcode Options
When you send inventory to an Amazon fulfillment center, every unit must have a scannable barcode. Amazon gives sellers two paths to compliance:
Option 1 — FNSKU label (default requirement): Amazon generates a unique Fulfillment Network SKU for each of your ASIN + condition combinations. You print that label and apply it to every unit before shipping to FBA. Amazon uses it to track your specific inventory, separate from other sellers' stock of the same product.
Option 2 — Manufacturer barcode exemption (UPC/EAN): If your seller account qualifies for the exemption, Amazon may allow you to use the product's existing UPC or EAN-13 barcode instead of an FNSKU label. This sounds convenient, but it comes with a significant catch: your units enter Amazon's commingled inventory pool and may be mixed with the same product from other sellers. If another seller's units have quality issues, your account can be affected.
The bottom line: most sellers — especially private-label and retail arbitrage sellers — should use FNSKU labels. The exemption makes sense only in specific brand-ownership scenarios described below.
What Is an FNSKU?
FNSKU stands for Fulfillment Network SKU. It is an identifier Amazon assigns exclusively to you for a specific product listing and condition. Here is what you need to know:
- Format: alphanumeric string, typically starting with "X" — for example,
X001ABCDEF - Barcode symbology: Code 128 (Amazon encodes FNSKUs using Code 128)
- One FNSKU per ASIN + condition: a "New" unit of ASIN B09XYZ123 gets a different FNSKU from a "Used — Like New" unit of the same ASIN
- Where to get it: Seller Central → Inventory → Manage All Inventory → select items → Print Item Labels. You can also find it on the product detail page in Seller Central.
- Cost: free — Amazon generates FNSKUs at no charge as part of your seller account
Once you have your FNSKU codes, you can paste the list into a barcode generator, choose Code 128, and print labels formatted for any standard label sheet.
When Can I Use UPC Instead?
Amazon calls this the Manufacturer Barcode Exemption. To qualify, you generally need to meet one of the following criteria:
- You are enrolled in Amazon Brand Registry and are the brand owner
- You are the manufacturer of the product and can demonstrate brand ownership
- Amazon has approved your product category for commingled inventory (certain media and simple commodity items)
If you qualify and opt into the exemption, your units ship without FNSKU stickers. Amazon identifies them by the UPC or EAN-13 on the original product packaging.
The risk is commingling: your units sit in the same bin as identical units from other sellers. If a counterfeit or defective unit enters the pool, Amazon cannot always distinguish whose stock is whose. For this reason, many brand-registered sellers still choose to apply FNSKU labels voluntarily — it keeps their inventory isolated and protects their seller metrics.
FNSKU vs UPC — Which Is Right for You?
| FNSKU | Manufacturer UPC / EAN | |
|---|---|---|
| Who needs it | Most FBA sellers (default) | Brand-exempt sellers only |
| Assigned by | Amazon (free) | GS1 (paid membership, $250+/yr) |
| Inventory mixing | No — your stock stays separate | Yes — commingled with other sellers |
| Risk of commingling issues | None | Possible — defective units from others can affect you |
| Private label sellers | Recommended | Allowed if brand registered |
| Retail / online arbitrage | Required | Usually not allowed |
| Wholesale resellers | Required (unless brand-exempt) | Rarely available |
If you are just starting out or are uncertain, default to FNSKU. It is free, protects your inventory, and is always accepted by Amazon.
Amazon FBA Barcode Label Requirements
Amazon publishes specific technical requirements for FBA item labels. Getting these wrong is one of the most common reasons for a shipment to be refused or relabeled at your expense:
- Minimum size: 1 inch × 2 inches (25 mm × 50 mm). Amazon recommends 1" × 2-5/8" — this matches the Avery 5160 template (30 labels per sheet).
- Barcode format: Code 128 for FNSKU; UPC-A or EAN-13 if you are using the manufacturer barcode exemption
- Human-readable text: the FNSKU must appear in plain text below the barcode, along with a product title (truncated if necessary)
- Colors: black bars on white background — no color barcodes, no dark backgrounds
- Paper finish: matte (non-glossy). Glossy labels reflect light and cause scan failures at Amazon's receiving stations
- Placement: the FNSKU label must fully cover any pre-existing barcode on the product or packaging. If the original UPC is still readable underneath, Amazon's scanner may pick up the wrong code.
- One label per unit: do not apply multiple barcodes to the same unit — if two barcodes are present and readable, Amazon may reject the shipment
How to Print FBA Barcode Labels for Free
There are two practical ways to print FNSKU labels, depending on your volume:
Method 1: Print directly from Seller Central
Seller Central has a built-in label printing tool under Manage Inventory → Print Item Labels. It prints up to 40 labels per item in a single batch, and supports a small set of label sheet formats. This works well for one-off shipments but becomes slow and tedious for large restocks or multi-SKU shipments.
Method 2: Export and print in bulk with a barcode generator (recommended)
For larger shipments, export your FNSKU list from Seller Central, paste it into a bulk barcode generator, and download a print-ready PDF formatted for Avery 5160 or your preferred label sheet. This method has no row limit and takes under a minute for hundreds of SKUs.
Export your FNSKUs from Seller Central
Go to Inventory → Manage All Inventory → select the products you are shipping → Actions → Print Item Labels. Copy the FNSKU codes from the preview, or download your inventory report which includes the FNSKU column.
Paste into Bulk Barcode Generator and select Code 128
Paste your FNSKU list (one per row) into the generator. Select Code 128 as the barcode type — this is the format Amazon requires for FNSKUs. Add the product name as the label text line if you want it to appear below the barcode.
Choose Avery 5160 layout and download PDF
Select the Avery 5160 label preset (1" × 2-5/8", 30-up on a standard letter sheet). Download the PDF and print on matte label paper. Each FNSKU gets its own label, ready to apply.
Got a list of FNSKUs from Seller Central? Paste them into Bulk Barcode Generator — select Code 128, choose the Avery 5160 layout, and download a print-ready PDF. Free, no signup, no row limit.
Print FBA Labels Free →Common Mistakes to Avoid
These errors consistently cause FBA shipments to be rejected or flagged during receiving:
- Two barcodes on one unit: if the original UPC is still visible under your FNSKU label, Amazon's scanner can pick up both. The label must fully cover any existing barcode.
- Font too small: Amazon requires the human-readable FNSKU text to be at least 8pt. Use 10pt or larger for reliable readability. Small text also suggests a low-quality print that may fail scanning.
- Glossy label paper: direct thermal labels are matte by design, but inkjet-printed glossy sheets will reflect the scanner beam. Always use matte finish adhesive labels.
- Printing FNSKU in the wrong barcode format: FNSKUs must be encoded as Code 128. If you accidentally select UPC-A or EAN-13, the barcode will not encode an alphanumeric string like X001ABCDEF — you will get an error or a garbled label.
- Using an outdated FNSKU: if you close and reopen a listing, or change the product condition, Amazon may assign a new FNSKU. Always check that your printed labels match the current FNSKU shown in Seller Central before shipping.
- Applying FNSKU labels after boxing: labels should be on individual units, not on the outer box (unless Amazon specifically requires a box label for a case-packed shipment).
Getting the basics right — Code 128 format, matte paper, full coverage of existing barcodes, current FNSKU — eliminates the vast majority of FBA receiving problems.