Understanding Amazon Product Codes

Introduction

Selling on Amazon means working with several product identifiers: SKU, ASIN, FNSKU, UPC/EAN/ISBN, and LPN. At first glance, they might look like random strings of letters and numbers, but each serves a unique role in cataloging, fulfillment, and returns.

If you don’t understand how these codes differ, you risk inventory errors, mislabeled shipments, or confusion when dealing with Amazon support. This guide breaks down the main identifiers and explains how they connect.

ASIN: Amazon Standard Identification Number

• What it is: Amazon’s catalog ID assigned to every product listing.
• Format: 10-character alphanumeric code (e.g., B01N5IB20Q)
• Scope: Global across Amazon. The same ASIN applies to all sellers offering the same product.
• Use case:
  • Defines a product in Amazon’s catalog
  • Required for listing creation
  • Appears in product URLs (after “/dp/”)

ASIN = what the product is on Amazon.

SKU: Stock Keeping Unit

• What it is: A seller-defined identifier used for internal tracking.
• Format: Customizable by you (e.g., 2023X-ABC123-WHT-L-BRK)
• Scope: Private to each seller. Different sellers can have different SKUs for the same ASIN.
• Use case:
  • Organizing inventory in your own system
  • Tracking variations like size, color, or warehouse
  • Linking supplier or batch data

SKU = how you manage it in your business.

FNSKU: Fulfillment Network SKU

• What it is: Amazon’s identifier for FBA inventory, tying products to your account.
• Format: Always starts with X (e.g., X001234567)
• Scope: Unique per seller-ASIN in the FBA system.
• Use case:
  • Printed on labels for items sent to FBA
  • Ensures Amazon ships your stock, not another seller’s
  • Used for reimbursements if inventory is lost or damaged

FNSKU = how Amazon tracks your stock in FBA.

UPC, EAN, and ISBN

These are global product codes used in retail and publishing, not just Amazon:

• UPC: 12-digit numeric code, common in the U.S.
• EAN: 13-digit code, common outside the U.S.
• ISBN: Assigned to books and book editions (10 or 13 digits).

Amazon typically requires one of these identifiers when creating a new listing, unless you qualify for GTIN exemption.

UPC/EAN/ISBN = how global retail and publishing identify products.

LPN: License Plate Number

• What it is: A unique identifier Amazon assigns to individual units, often for returns or damaged goods.
• Format: Alphanumeric, beginning with LPN (e.g., LPN1234ABCDEF)
• Scope: Tracks a single item in Amazon’s system, not reusable.
• Use case:
  • Applied to returned or problem units in fulfillment centers
  • Used internally for investigations and reimbursements
  • Helps sellers when working with Amazon support on returns

LPN = how Amazon tracks individual returned or damaged units.

How They Work Together

Here’s how these identifiers might line up for a single product:

• You list a red water bottle.
• Amazon assigns it an ASIN: B01234ABCX
• You assign your own SKU: WTR-RD-20OZ
• For FBA, Amazon generates an FNSKU: X001ABCDEF
• The product has a UPC: 012345678905
• A customer returns one, and Amazon gives it an LPN: LPN987654321

The chain looks like this:

WTR-RD-20OZ (SKU) → B01234ABCX (ASIN) → X001ABCDEF (FNSKU) → 012345678905 (UPC) → LPN987654321 (return tracking)

Comparison at a Glance

Closing Thoughts

Each code plays a different role in keeping Amazon’s ecosystem organized:

• ASIN = what the product is
• SKU = how you manage it internally
• FNSKU = how Amazon FBA tracks your stock
• UPC/EAN/ISBN = how global retail and publishing identify products
• LPN = how Amazon tracks individual returned units

When you understand how they connect, you’ll avoid costly errors and make your Amazon business easier to manage.

About the Author

Becky Phipps runs a 7-figure Amazon business from her garage, where she has mastered product sourcing, logistics, and scaling e-commerce brands. With over 15 years of experience selling online, she shares insights on entrepreneurship, marketing, and the realities of building a business from the ground up. Outside of work, Becky is an avid plant-grower, book-reader, and mom.