GTIN, MPN and SKU are three product identifiers with different jobs. A GTIN is the globally unique barcode number for a product, and an MPN is the manufacturer's part number. Both let a machine match your listing to the same item on other sites, while a SKU is your own stock code and means nothing outside your store.
Identity is one of the first questions a machine asks about a product: is this the exact item the shopper means, and is it the same item that has reviews and prices elsewhere? Identifiers answer that question directly. Without them, a machine has to match on the product name alone, which works badly for anything sold under more than one name.
What is the difference between GTIN, MPN and SKU?
| Identifier | What it is | Who assigns it | Why AI needs it |
|---|---|---|---|
| GTIN | Global trade item number (barcode) | The manufacturer / GS1 | Match to the exact product worldwide |
| MPN | Manufacturer part number | The manufacturer | Match across resellers of the same item |
| SKU | Stock-keeping unit | You | Your internal tracking, not a global match |
- A GTIN, or Global Trade Item Number, is the number behind a product's barcode. GS1 describes it as a globally unique number used to identify a trade item, issued exclusively by GS1, and assigned to the product by the brand owner. UPC and EAN codes are both GTINs.
- An MPN, or manufacturer part number, identifies a product for a given manufacturer. It matters most when a product has no GTIN, which is common for parts and made to order goods.
- A SKU, or stock keeping unit, is the code you use to track stock. Shopify's help center says SKUs identify products within your business, so they do not help a machine match you to anyone else.
Why do identifiers matter for AI and Google?
Google's guide to merchant listing markup lists gtin, mpn and brand among the recommended properties of a Product, and asks you to include all applicable global identifiers. Identifiers are how separate listings of the same product connect, so a product with a correct GTIN can be matched to the same item on other sites that list it.
Most stores have work to do on this layer. Our June 2026 study scored 216 Shopify storefronts, and 72% of them failed the product and brand structured data part of the score.
Where do I add identifiers on Shopify?
- In your Shopify admin, go to Products and open a product.
- If the product has variants, click a variant. Each variant has its own SKU and barcode, since each size or color has its own GTIN.
- In the Inventory section, enter the SKU and the barcode. Use the GTIN printed on the product or given by the brand owner, never a number you made up.
- Click Save, then repeat for each variant.
- For brand, use the Vendor field on the product, which many themes print as the brand in structured data. Check yours in step 7.
- For MPN, ask your developer or theme provider whether your theme prints a metafield as mpn. If it does not, a developer can add it to the product structured data in a duplicate of your theme.
- Open the product page, paste its address into Google's Rich Results Test, and check that the Product shows the gtin and brand you entered.
Start with your best sellers. A product made in your own workshop with no barcode should leave gtin out, since an invented number is worse than none.
How does a coffee equipment store get its boxed UPC codes into Shopify?
A coffee equipment store on Shopify resells grinders and kettles from four manufacturers, about 80 products in all. Every variant has a SKU, such as GR-BLK-01, and no barcode. The boxes in the stockroom all carry printed UPC codes.
The owner types the UPC from each box into the barcode field of each variant, puts the manufacturer's name in Vendor, and asks the developer to print the model number from a metafield as mpn. The Rich Results Test now shows gtin, mpn and brand on every grinder. The answer had been printed on the side of every box in the stockroom.
How do identifiers fit with the rest of the product data?
Identifiers are one of the fields that separate a bare Product from a complete one, as product schema that gets you compared shows. For the Google Merchant Center side, read which Merchant Center attributes and GTINs Google's AI shopping results read. The description and title that sit beside the codes are covered in product descriptions for AI and product titles AI can match, and entity recognition applies the same idea to your brand.
The Agency plan reads 600 pages of your store on every scan, product pages included, and lists every product whose structured data leaves out an identifier you could add.
Questions owners ask
What is the difference between GTIN, MPN and SKU?
A GTIN is the globally unique barcode number for a product, and an MPN is the manufacturer's part number. A SKU is your own stock code, which helps you track inventory but means nothing outside your store.
Why do product identifiers matter for AI?
Identifiers let a machine confirm that your listing is the same item as listings elsewhere. Google lists gtin, mpn and brand among the recommended properties for merchant listing markup.
Where do I add a GTIN on Shopify?
Open the product in Products, click the variant, and enter the GTIN in the barcode field of the Inventory section. Each variant needs its own number.
What if my product has no barcode?
Leave the GTIN out rather than invent one. Declare the brand, and the MPN if the manufacturer gives one, so a machine still has something true to match on.
Sources
We opened every source below on November 9, 2026.
- What is a GTIN?, GS1 US.
- Merchant listing structured data, Google Search Central.
- Product variants, Shopify Help Center.
- The State of AI Visibility 2026, Visibility Mesh, 216 Shopify storefronts scored in June 2026.