Product Identifiers, Explained Simply: UPC, EAN, GTIN, ASIN, ISBN, and SKU

A product identifier is a unique code assigned to a product so that systems, stores, and marketplaces can recognize it without reading the name. Some identifiers are universal standards shared by everyone, like the UPC and EAN managed through GS1. Others are private, like Amazon's ASIN or a store's internal SKU.

A UPC, short for Universal Product Code, is the 12-digit barcode printed on most products sold in North America. Brands get UPCs by licensing a company prefix from GS1, the not-for-profit body that runs the global barcode system. The final digit is a check digit, a small piece of math that catches typing and scanning mistakes.

Barcodes have been doing this job for a long time. GS1 records the first ever retail barcode scan on 26 June 1974, a pack of Wrigley's chewing gum at a supermarket in Troy, Ohio. The system has identified products the same basic way ever since.

You can check any UPC with the free UPC lookup, and our complete UPC guide goes deeper into formats and prefixes.

An EAN, or International Article Number, is the 13-digit version of the same GS1 system, and it is the standard barcode outside the United States. A US product often carries a 12-digit UPC at home and is stored as a 13-digit EAN abroad by adding a leading zero. Small packages use the short EAN-8 format.

If a supplier in Europe quotes you a 13-digit code, it is an EAN. Check it with the free EAN lookup.

GTIN stands for Global Trade Item Number. It is not a different code. It is the family name for the whole GS1 system: GTIN-12 is the UPC, GTIN-13 is the EAN, GTIN-8 is the short EAN, and GTIN-14 marks cartons and cases.

This matters because platforms ask for it by this name. Google requires a GTIN for most new products in Shopping listings (Google Merchant Center Help). If a form asks for a GTIN, enter your UPC or EAN. That is the answer. Our GTIN vs UPC page and the GTIN requirements guide for Google Shopping cover the details, and the GTIN lookup checks any code.

An ASIN, or Amazon Standard Identification Number, is the 10-character code Amazon assigns to every product in its catalog. Most start with B0. You will find it in the product page address after /dp/ and in the Product Information section. For most books, the ASIN is simply the ISBN-10.

The key thing to remember: an ASIN means nothing outside Amazon. The same product lives in the rest of retail under its UPC or EAN. That is why sellers constantly convert between the two, using an ASIN to UPC converter in one direction and a UPC to ASIN converter in the other. To inspect any Amazon product, use the free ASIN lookup tool, or read what is an ASIN for the full story.

An ISBN, or International Standard Book Number, identifies books and editions. Since January 2007 new ISBNs have 13 digits and start with 978 or 979 (International ISBN Agency). Older books carry 10-digit ISBNs, and Amazon uses that ISBN-10 as the book's ASIN. Check any book code with the ISBN lookup.

A SKU, or stock keeping unit, is a code a business invents for its own shelves. TSHIRT-BLU-M is a SKU. There is no SKU registry and no standard format, which is why the same product has a different SKU in every store that sells it. Connecting a SKU to universal codes is a lookup job: match the product once by name or barcode, then save the pairing. Start with the free SKU lookup.

Picture one pair of wireless earbuds. The factory prints an EAN barcode on the box. In a US store system the same product sits under its UPC. Google Shopping stores that code as a GTIN. Amazon files the product under an ASIN. And the warehouse that ships it calls it EB-BLK-01, its own SKU. Five names, one product. Product data tools exist to keep those five names pointing at the same item.

No. Under GS1 rules each sellable variation gets its own GTIN, so a medium blue shirt and a large blue shirt carry different codes. If a scan brings up the wrong product, the listing data is wrong, not the system. The check digit only catches typos. It cannot catch a code assigned to the wrong item, which is why marketplaces lean on clean product data.

Conversion is really a lookup. The codes are linked in a catalog, and a converter finds the record where they meet. The free tools handle each direction:

• Have an ASIN, need the barcode: ASIN to UPC converter.
• Have a barcode, need the Amazon listing: UPC to ASIN converter.
• Have a name, model, or partial code: barcode lookup search.
• Have a whole spreadsheet: bulk barcode lookup, or the product data API for anything automated.

Marketplaces demand it. Amazon lists by ASIN but asks for a GTIN when you create a product. Google Shopping requires GTINs for most products.

Matching drives sourcing. Buying stock means matching a supplier's EAN to an Amazon ASIN before you commit money.

Clean data compounds. Duplicate and mismatched identifiers cause lost listings, wrong shipments, and messy analytics. Our piece on product data quality for AI explains why this is getting more important, not less.

Machines read codes, not names. Search engines, marketplaces, and AI shopping agents all resolve products by identifier first.

The last digit of every UPC and EAN is calculated from the others, so scanners can catch mistakes. Take the famous first-scan UPC, 036000291452. Add the digits in the odd positions (0+6+0+2+1+5 = 14) and multiply by three to get 42. Add the even-position digits (3+0+0+9+4 = 16) for a total of 58. The check digit is whatever lifts that total to the next multiple of ten. 58 needs 2 to reach 60, and 2 is exactly the final digit. Change any single digit and the math breaks, which is how a typo announces itself.

Walk into a warehouse and the boxes carry a 14-digit code even though the products inside carry 12 or 13. That is GTIN-14, the packaging-level member of the family. It wraps the product GTIN with an extra indicator digit that marks the packaging level, so a case of 24 units has a different code than the single unit inside it. If a warehouse scan resolves to the wrong quantity, a case code being read as a unit code is the usual reason.

The barcode is the picture. The identifier is the number inside it. That difference matters because the picture is changing: GS1 is moving retail toward 2D codes like QR-style symbols, with an industry ambition for retail checkout to accept them by the end of 2027, an initiative GS1 US calls Sunrise 2027. The numbers inside, the GTINs, stay the same. Learn the identifiers and the packaging can change around you without breaking anything you built.

• Typing the check digit from memory. If a lookup fails, re-scan or re-read the digits from the package before assuming the product is missing.
• Putting a SKU where a GTIN belongs. Marketplace forms want the universal code. Your internal code means nothing to their catalog.
• Reusing one GTIN across variants. Each size and color needs its own code, and channels reject catalogs that break this rule.
• Treating an ASIN as permanent and global. Amazon can merge listings, and the same product can carry different ASINs in different marketplaces.
• Buying codes from unofficial resellers. GS1 licenses prefixes to brands directly. Codes from other sources can collide with existing products, and marketplaces check.

Every identifier in this guide has a free lookup tool: UPC, EAN, GTIN, ISBN, ASIN, and SKU. Each includes 10 free lookups per day, no signup. Developers can use the barcode lookup API.