If you’re selling on Amazon, barcode confusion can slow you down fast. UPC? FNSKU? ASIN? It’s easy to mix them up.
So let’s clear it up.
Amazon primarily uses FNSKU barcodes for seller inventory tracking, while UPC, EAN, or ISBN codes are used for product identification.
That’s the short version. Now let’s explain what that actually means.
When listing and shipping products to Amazon, you’ll encounter two key barcode formats:
• 12-digit barcode
• Used globally for retail products
• Required when creating most new product listings
• Identifies the product itself
Think of UPC as the product’s universal ID. If multiple sellers offer the same item, they’ll typically share the same UPC.
• Unique barcode generated by Amazon
• Used for FBA (Fulfillment by Amazon)
• Identifies your specific inventory
Here’s the key difference:
A UPC identifies the product.
An FNSKU identifies the seller’s inventory.
If you’re using FBA, Amazon usually requires you to label your products with an FNSKU so your stock doesn’t get mixed with another seller’s inventory.
Not always.
It depends on your fulfillment method:
✅ If You Use FBA (Fulfillment by Amazon)
Amazon typically requires:
• An FNSKU label on each unit
• Barcode placed over the manufacturer’s UPC (if commingling is disabled)
This ensures your inventory is tracked correctly inside Amazon warehouses.
✅ If You Use FBM (Fulfilled by Merchant)
You can often use:
• The original UPC barcode
• No additional Amazon barcode required
Since you ship products yourself, Amazon doesn’t need warehouse-level tracking labels.
You’ll also hear about ASIN.
ASIN stands for Amazon Standard Identification Number.
• Every product listed on Amazon has an ASIN.
• It’s used internally by Amazon.
• It’s not typically printed as a scannable barcode for shipping.
So while ASIN is important for listings, it’s not the barcode format you print on product packaging.
Here’s a simple breakdown:
| Selling Method | Barcode to Use |
| FBA Seller | FNSKU |
| FBM Seller | UPC (usually) |
| Private Label | UPC + FNSKU |
| Bundled Products | New UPC required |
If you’re shipping products into Amazon warehouses, expect to print FNSKU labels. Most sellers use 4" × 6" or 2" × 1" barcode labels for this purpose.
Using the wrong barcode can cause:
• Inventory mix-ups
• Receiving delays
• Product misplacement
• Listing suppression
In short, not ideal.
Amazon’s system is automated. If the barcode doesn’t match what’s expected in Seller Central, your shipment can get flagged.
Better to get it right the first time.
Technically, no. You can print FNSKU labels with a standard inkjet or laser printer.
But if you’re shipping regularly, a thermal barcode printer makes life easier:
• No ink smudging
• Faster batch printing
• Lower cost per label
• Better scan reliability
For small batches, a regular printer works fine. For consistent FBA shipments, a thermal printer saves time and hassle.
Can I use the manufacturer barcode instead of FNSKU?
Sometimes, if Amazon allows commingled inventory. But many sellers disable this for better control.
Do I need to cover the UPC?
Yes, if you’re using FNSKU labels for FBA. The scannable barcode must match Amazon’s system.
Can I generate FNSKU codes myself?
No. Amazon generates them inside Seller Central.
Amazon uses multiple barcode formats—but for most FBA sellers, FNSKU is the barcode that matters for inventory tracking, while UPC identifies the product itself.
If you’re serious about selling on Amazon, understanding the difference keeps your inventory flowing smoothly and avoids costly mistakes.
Get the barcode right, and the rest gets a whole lot easier.