# What is a GTIN and what is it used for? > What a GTIN is, its formats (GTIN-13 or EAN, GTIN-12, GTIN-8, GTIN-14), who assigns it, how it goes on a product page and why you never make one up. URL: https://clione.ai/glossary/gtin/ Lang: en If you sell other brands' products, the GTIN already exists: it is the number under the barcode on the box. It is not your internal reference, the [SKU](/glossary/sku/), nor the manufacturer's catalog reference, the [MPN](/glossary/mpn/), nor exactly the [EAN code](/glossary/ean-code/), which is the barcode symbol that carries it. It matters to you because it is **how Google and the other channels know your product is the same one another store sells**: without it, or with a wrong one, Google warns that your product may have limited visibility.[^google-mc-gtin] ## How it works GS1, the organization that maintains the standard, defines GTINs as unique, universal and unambiguous numberings that identify trade items, meaning products or services that have a price and can be invoiced and bought at any point in the supply chain. **A GTIN can only be generated from a GS1 company prefix**, and the last digit is always a check digit.[^gs1es-gtin] GS1 US sums it up this way: it is a number GS1 issues exclusively and that all retailers, distributors and marketplaces in the world use to identify the same product, while each store gives it its own SKU for its inventory.[^gs1us-gtin] There are four lengths, each with its use:[^gs1es-gtin] | Type | Digits | What it is used for | | ------------- | ------ | ------------------------------------------------------------------------------------------------------------------------------------- | | GTIN-13 | 13 | Units sold to the end consumer, and also cases or pallets. It is the common retail format, and it is sometimes requested as "EAN-13". | | GTIN-12 (UPC) | 12 | The equivalent of the GTIN-13 in the US market. | | GTIN-8 | 8 | Very small items, whose packaging has no room for a longer code. | | GTIN-14 | 14 | Logistics groupings (cases, pallets) of a product that already has its GTIN-13. | **The check digit** is what makes it possible to detect a mistyped number. GS1 Spain explains the calculation in three steps: number the digits from right to left, multiply by 3 the ones in odd positions and by 1 the ones in even positions, add up the results and subtract that sum from the next multiple of ten. What is left is the check digit.[^gs1es-digito] **At Google** the GTIN comes in through two doors. In the [product feed](/glossary/product-feed/) for [Google Merchant Center](/glossary/google-merchant-center/), Google recommends it for every product that has a manufacturer-assigned GTIN, ideally together with the MPN, and sets clear conditions: **only if you are sure it is correct**, with the check digit properly calculated, outside the restricted ranges (prefixes 02, 04 or 2) and the coupon ones (05, 98 or 99), and a different one for each color or size [variant](/glossary/product-variants/).[^google-mc-gtin] In the [structured data](/glossary/structured-data/) of the [product page](/glossary/product-page/) it goes in the [Product](/glossary/product-schema/) node. [Schema.org](/glossary/schema-org/) defines the `gtin` property for values of 8, 12, 13 or 14 digits with a valid check digit, and presents it as the generalization of `gtin8`, `gtin12`, `gtin13` and `gtin14`.[^schema-org-gtin] Google accepts the generic one, but recommends the most specific one that fits the product, because it is the most exact representation, and it only accepts the number, not the URL form.[^google-merchant-listing] ## In a store What you need to know is where each product's number comes from. **Fictitious example**: the store and the products are invented, and the last column applies Google Merchant Center's rules.[^google-mc-gtin] | Product | Does it have a GTIN? | What gets sent | | ------------------------------------------------- | ------------------------------------------- | --------------------------------------------------------------------- | | A camera from a well-known brand | Yes, the manufacturer's, printed on the box | That number, as is, and the same one in the feed and on the page | | The same camera in black and in silver | Yes, one per color | Each [product variant](/glossary/product-variants/) with its own GTIN | | A private-label T-shirt that only you sell | Normally not | Nothing: Google says you do not need to send one | | A three-pack of identical units that you assemble | The unit's | The individual product's GTIN, MPN and brand | | A camera with a bag and a card that you bundle | The camera's | The main product's identifiers | And the check digit, calculated by hand with GS1's method on a made-up number: **2001234567893**.[^gs1es-digito] It starts with 2 on purpose, a prefix from the restricted range that Google does not accept in a feed,[^google-mc-gtin] so nobody mistakes it for a real product. ```text Digits (without the check digit): 2 0 0 1 2 3 4 5 6 7 8 9 Weight, from the right: 1 3 1 3 1 3 1 3 1 3 1 3 Product: 2 0 0 3 2 9 4 15 6 21 8 27 Sum: 97 · next multiple of ten: 100 · check digit: 100 - 97 = 3 ``` If your catalog has a GTIN that is missing a digit or whose last digit does not match this calculation, the number is wrong, and the right thing is to ask the manufacturer for it, not to fix it by eye. Filling in the GTIN field with the SKU, or with any number, to make a warning go away. Google says the opposite: if you are not sure about a GTIN, do not send it, do not guess it or invent it; and if the product is private-label or only you sell it, it normally has no GTIN and you do not need to send one.[^google-mc-gtin] ## How to check it 1. **Count the digits.** A valid GTIN has 8, 12, 13 or 14, with no letters.[^schema-org-gtin] 2. **Recalculate the check digit** with GS1's calculator or with the three-step method.[^gs1es-digito] 3. **Look it up in Verified by GS1.** With the product's number, the lookup returns the data of the company that owns the brand.[^gs1es-buscador] If it is not the brand you sell, something is wrong. 4. **Look at the prefix.** Those starting with 02, 04 or 2 are restricted circulation, and those starting with 05, 98 or 99 are coupons: Google does not accept them as a GTIN.[^google-mc-gtin] 5. **Compare variants and channels.** Each size and each color, its own number; and the same number in the feed and in the page's `gtin13` markup.[^google-mc-gtin][^google-merchant-listing] ## Related concept: EAN code Many people say "the EAN" when they mean the GTIN, and for day-to-day purposes it makes no difference. The difference is this: **the GTIN-13 is the number; the EAN-13 is the barcode that represents it**, and GS1 Spain warns that one is sometimes requested in place of the other.[^gs1es-gtin] Google Merchant Center treats them as the same for the feed: an EAN is, to it, a 13-digit GTIN-13.[^google-mc-gtin] Where the difference matters is on the physical label: the symbol can be printed badly or at a size the scanner cannot read, and the number still be correct. The [EAN code](/glossary/ean-code/) entry covers the symbol; this one, the number. To go on, the [structured data reading path](/learn/structured-data/) puts the rest of the terms in order, and the [Product](/glossary/product-schema/) entry explains where the GTIN and the other identifiers go on the page.