GTIN

Each GTIN combines a GS1 Company Prefix, an item reference, and a calculated check digit. The number is the data; the barcode is only the carrier. The same product keeps the same GTIN whether it is scanned at a till, listed on Amazon, or submitted in a Google product feed.

Formats and naming

GTIN-12 is what North America calls a UPC. GTIN-13 is the EAN used in most of the rest of the world. GTIN-8 covers small packages, and GTIN-14 identifies case or carton groupings and never starts with zero. UPC and EAN are not separate systems, they are shorter GTINs carried in different barcode symbologies.

For SEO the load-bearing part is matching. Google Merchant Center treats the GTIN as the key that ties your listing to a canonical product entity: identifiers “uniquely distinguish products you’re selling and help match search queries with your products.” If a product has a manufacturer-assigned GTIN and you leave it out, Google says the listing “may have limited visibility,” and submitting a wrong one can get the product disapproved. Every variant (each color, each size) needs its own GTIN, not one shared across the set.

Rule of thumb: only submit a GTIN you can verify against the manufacturer or the packaging. Do not guess. A made-up value can still pass the check-digit test while pointing at the wrong product, which is worse than leaving the field blank.