Product Identifiers Explained: GTIN, MPN and Brand in Google Merchant Center

Google Merchant Center asks for three product identifiers: GTIN, MPN and brand. Together Google calls them unique product identifiers (UPIs). They tell Google exactly which product you’re selling, independent of how you describe it.

This guide explains what each identifier is and how they fit together. If Merchant Center is already showing an identifier issue, go straight to how to fix missing product identifiers.

What unique product identifiers are

Google’s unique product identifier documentation describes UPIs as identifiers assigned by the manufacturer. Because the manufacturer assigns them, they’re identical across every retailer that sells the product. A particular pair of headphones has the same GTIN whether it’s sold by a big-box store or a small independent shop.

That’s the key difference from the rest of your feed. Your title, description and product ID are yours; you write them. Identifiers aren’t yours to choose (with one exception, covered below for products you make yourself).

Identifier	What it is	Who assigns it
GTIN	Global Trade Item Number: the number behind a product’s barcode	Manufacturer
MPN	Manufacturer Part Number: an alphanumeric code the manufacturer uses	Manufacturer
Brand	The brand name associated with the product	Manufacturer or brand owner

Google recommends submitting all three when they exist. The minimum is set by Google’s rules: brand plus GTIN, or brand plus MPN when no GTIN was assigned.

Why Google uses identifiers

Identifiers let Google recognize that your product is the same item other sellers list, even when titles differ. In practical terms, Google’s documentation connects them to visibility and approval:

• Google recommends GTINs, and products that have an assigned GTIN but are submitted without it may have limited visibility.
• Incorrect identifiers may cause disapproval, so a wrong GTIN is worse than none.
• The Shopping Knowledge Panel, a free listings surface available in the US and some other countries, needs strong identifiers, according to Google’s free listings documentation.
• Google Search Central lists gtin, mpn and brand among the recommended properties in merchant listing structured data.

GTIN: the barcode number

A GTIN is the number encoded in a product’s barcode. Several numbering systems are all types of GTIN, and Google accepts each:

Type	Length	Where it’s used
UPC (GTIN-12)	12 digits	North America
EAN (GTIN-13)	Typically 13 digits; sometimes 8 or 14	Mainly outside North America
JAN	8 or 13 digits	Japan
ISBN	ISBN-13 recommended (starts with 978 or 979); ISBN-10 deprecated since 2007	Books

For a US store, most branded products from North American manufacturers carry a 12-digit UPC. Imported products often carry a 13-digit EAN. Both are valid GTINs; submit the one printed on the product rather than converting between them.

Where to find a GTIN

• Printed under the barcode on the product or its packaging.
• In the product data your supplier or distributor provides.
• On the manufacturer’s spec sheet or product information files.

Practitioner tip: each variant usually has its own GTIN. A shirt in three sizes typically has three different barcodes, so each variant record in your feed needs its own value.

Products that often have no GTIN

Google lists examples of products that commonly don’t have a GTIN: store brands, replacement parts, OEM parts, custom-made goods, books published before 1970, vintage and antique items, and pre-order products. “Often” isn’t “always”, so check before deciding a product has none.

Brand: whose product it is

The brand attribute is the brand associated with the product, not the store selling it. For a reseller, that’s the manufacturer’s brand. For your own private-label range, it’s your brand.

• Brand isn’t needed for products with no clearly associated brand. Google gives movies, books and music as examples.
• If you make the product yourself (custom or handmade) and have no official brand, Google says to use your store name as the brand.
• Practitioner tip: on many platforms the brand is taken from a “vendor” or “manufacturer” field. Check it holds the real brand rather than a distributor’s company name.

MPN: the manufacturer’s part number

An MPN is an alphanumeric code the manufacturer uses to identify the product. It’s most common for parts, components, tools and electronics, where the part number is how buyers search.

MPN matters most when there’s no GTIN. In that case Google’s rule is brand plus MPN. If you manufacture the product yourself, Google lets you assign an MPN of your choice alongside your store name as brand. Practitioner tip: once assigned, keep that MPN stable and unique to each product.

identifier_exists: when there are no identifiers

The identifier_exists attribute tells Google whether a product has manufacturer identifiers. Google’s GTIN fix article says to set it to false for one-of-a-kind or vintage products. When no identifiers were assigned, don’t include gtin, brand or mpn, and don’t fill them with SKUs.

It’s not a way to silence warnings on branded products. If a product has a GTIN, setting identifier_exists to false is incorrect and gives up the benefit identifiers provide.

Identifiers vs your own IDs and SKUs

Feeds contain several ID-like values, and mixing them up is a common source of errors.

Value	What it is	Who sets it	Feed attribute
Product ID	Your unique key for each product in Merchant Center	You	id (Google recommends using the SKU)
SKU	Your internal stock-keeping code	You	Often used as id; never as gtin or mpn
Item group ID	Shared ID for all variants of one product	You	item_group_id (often the parent SKU)
GTIN	Global barcode number	Manufacturer	gtin
MPN	Manufacturer part number	Manufacturer (or you, for your own products)	mpn
Brand	Brand name	Brand owner	brand

Google is clear that if a GTIN exists but isn’t available to you, you should leave the field blank rather than submitting an internal SKU, and that identifiers shouldn’t be made up, guessed or copied from similar products.

Which identifiers a product needs

In short:

• Branded product with a barcode: gtin and brand, plus mpn if you have it.
• Branded product without a GTIN: brand and mpn.
• Your own custom or handmade product with no official brand: your store name as brand and an MPN you choose.
• One-of-a-kind or vintage item with no identifiers: identifier_exists = false.

The full decision table, including books, media and products whose GTIN you can’t find, is in how to fix missing product identifiers, along with Shopify and WooCommerce field locations.

Identifiers in structured data

The same identifiers should appear in your product page’s Product markup. Google Search Central lists these as recommended properties in its merchant listing structured data documentation:

Feed attribute	Structured data property	Note
gtin	gtin, gtin8, gtin12, gtin13, gtin14 or isbn	Numeric values
mpn	mpn
brand	brand.name
id (SKU)	sku
item_group_id	inProductGroupWithID	For variants

Keeping feed and markup consistent avoids sending Google conflicting signals. See how product structured data supports Shopping.

Common misconceptions

Misconception	Reality
“Any unique number will do for GTIN.”	GTINs must be the manufacturer-assigned values. Made-up or guessed values may cause disapproval.
“My SKU is my MPN.”	Not unless you’re the manufacturer. Internal SKUs shouldn’t be submitted as identifiers.
“I can copy the GTIN from a similar product.”	Google says not to copy identifiers from similar products.
“identifier_exists = false makes the warning go away, so it’s fine.”	It’s only for products that truly have no identifiers.
“Brand means my store name.”	Only for products you make with no official brand. Otherwise it’s the product’s brand.
“One GTIN covers all sizes and colors.”	Variants usually have their own GTINs; submit each variant’s own value.

When to get help

Identifier work is mostly about clean source data and correct mapping. If your supplier data is incomplete, your platform maps the wrong fields, or thousands of products show limited visibility, our product feed optimization service can trace and fix it. For active issues, start with the identifier fix guide or the disapprovals guide.

Frequently asked questions

Sources

• Google Merchant Center Help — About unique product identifiers
• Google Merchant Center Help — How to fix: Missing or incorrect GTIN
• Google Merchant Center Help — Product data specification
• Google Merchant Center Help — Free listings for products
• Google Merchant Center Help — ID [id]
• Google Merchant Center Help — Item group ID [item_group_id]
• Google Search Central — Merchant listing structured data

Last reviewed October 10, 2026 against the official documentation listed above. Google changes Merchant Center features and policies regularly — always confirm details in your own account.