FNSKU vs UPC vs SKU: Barcodes Explained for Sellers

Sellers use three codes constantly and sometimes interchange them: SKU, UPC and FNSKU. They look similar, but each answers a different question, and mixing them up is a common cause of receiving delays and inventory mix-ups. Here is the plain-language version.

SKU: your internal code

A stock keeping unit (SKU) is an identifier you create for your own inventory system. It can follow any logic you like, for example brand-style-size-color. It is not standardized, and two companies can use the same SKU for different products.

Used for: internal tracking, warehouse locations, order management, reporting.

UPC: the universal product code

A Universal Product Code is a standardized barcode that identifies a product across retailers, typically assigned through GS1. The same product carries the same UPC wherever it is sold. For more background, see our GS1 barcodes and product labeling guide.

Used for: retail scanning, marketplace listing, catalog matching.

FNSKU: Amazon’s fulfillment label

A Fulfillment Network SKU is an Amazon-assigned code tied to a specific product and seller. When inventory goes to Amazon’s fulfillment network, the FNSKU label lets Amazon identify whose item it is, and it can matter when products are commingled or not.

Used for: Amazon FBA inbound labeling and tracking. Amazon’s current rules on labeling and commingling change over time, so confirm in your Seller Central account.

Side-by-side

Where mistakes happen

1. Wrong label on the unit. A UPC is scanned where an FNSKU was needed, and Amazon cannot match the unit to your listing.
2. Duplicate SKUs. Two products share one SKU, so counts drift.
3. Old labels left on. Repackaged or relabeled goods show two barcodes, and the scanner reads the wrong one.
4. Bundles. A multipack needs its own identifier and labeling, not a loose unit’s code.

What a 3PL or prep center does

A good warehouse receives against your SKU, verifies quantities and applies the correct labels before items move to Amazon or to a retail customer. Typical services include:

• Applying FNSKU labels and covering old barcodes
• Polybagging and bundling
• Relabeling and rework. See Amazon FBA prep in Miami
• Syncing SKUs between your store and our inventory management system

Setup tips

• Keep a master SKU list that maps SKU to UPC and FNSKU.
• Decide your SKU naming rules once and stick to them.
• Send an advance shipping notice with SKU-level quantities so receiving is faster. See how to prepare inbound freight for receiving.

Work with us

If you sell on Amazon and other channels, our e-commerce fulfillment team can handle labeling and storage. Request a quote.

Frequently asked questions

Is an FNSKU the same as a UPC?

No. A UPC is a universal product barcode, while an FNSKU is an Amazon-assigned label tied to a product and seller within Amazon’s fulfillment network.

Do I need a UPC to sell on Amazon?

Many listings require a product identifier such as a UPC, though exemptions exist. Check Amazon’s current requirements in Seller Central.

Can a 3PL apply FNSKU labels for me?

Yes. Many 3PLs and prep centers apply FNSKU labels, cover old barcodes and prepare units before they ship to Amazon.