A Global Trade Item Number (GTIN) is the unique number behind a product’s barcode, used worldwide to identify one specific product from one specific brand. In the UK you most often see it as the 13-digit EAN printed under the barcode on packaging; books carry an ISBN, which is also a form of GTIN.
How a GTIN works
GTINs are issued through GS1, a not-for-profit standards body with a national organisation in each country. In the UK, brands join GS1 UK, receive a company prefix and use it to create a number for each product they make. Every distinct product and variant needs its own number: a red T-shirt in medium and the same T-shirt in large have different GTINs.
Several lengths are in use:
- GTIN-13 (EAN-13): the standard format in the UK and Europe.
- GTIN-12 (UPC): mainly on products made for North America.
- GTIN-8 (EAN-8): on very small packs.
- GTIN-14: on outer cases and multipacks in wholesale.
The GTIN belongs to the product, not to the shop selling it. If you resell a branded product, you use the manufacturer’s GTIN; you do not create your own. Your SKU is something else: a code you choose for your own stock control, in whatever format suits you.
Why it matters for a UK business
For online sellers, the main reason is Google. Google Merchant Center asks for a GTIN on every product that has one assigned by its manufacturer, because the number lets Google match your listing to the exact product in its database. That match connects your offer with reviews, specifications and other sellers’ prices, and helps Google show your listing to people searching for that exact item.
Products submitted without a valid GTIN, where one exists, can have limited visibility in Shopping ads and free listings, and Merchant Center flags them in its diagnostics. Wrong GTINs are worse: a number copied from another variant, or invented to fill the field, can cause disapprovals and mismatched listings.
Marketplaces rely on GTINs too. Amazon generally requires one to create a new listing unless the brand has an exemption, and eBay asks for product identifiers on new branded items in many categories.
Common mistakes
- Buying cheap barcodes from resellers. Numbers sold outside GS1 may be registered to another company, so Amazon and other retailers can reject them.
- Using one GTIN for every variant. Each size and colour needs its own number.
- Putting the SKU in the GTIN field. It fails validation and confuses product matching.
- Leaving the field empty when a GTIN exists. This happens often when product data is typed in by hand from supplier spreadsheets.
- Making up numbers for own-brand goods. If your handmade or own-label products have no GTIN, say so in the feed rather than filling the field.
How to act on it
For branded products you resell, ask each supplier for a spreadsheet of GTINs by variant and import it into your platform’s barcode field, which most platforms map to the feed automatically. For your own products, decide whether you need GTINs at all. If you plan to sell through retailers or on Amazon, join GS1 UK. If you only sell on your own site, you can usually leave them out, send the brand and a manufacturer part number (MPN) instead, or set the identifier exists attribute to “no”.
Then check the product feed diagnostics in Merchant Center for missing or invalid identifier warnings, and fix them in the source data rather than only in the feed, so they stay fixed.
Product identifiers are among the first things I check when a shop’s Shopping results are weak. My Performance Max management covers feed quality as well as the campaigns built on it.