GTIN, MPN and Brand Fields: Product Identifiers

A GTIN is the globally recognized number for a product. If the manufacturer assigned one, enter it in a valid format. If not, do not invent one: submit the brand and the MPN instead. A SKU is your own stock code and does not replace either field. For kitchen knives, that means a chef's knife from a known maker carries the maker's GTIN, a house-brand paring knife carries brand and MPN, and a boxed knife block set carries identifiers that depend on who put the set together.

The rules come from the Merchant Center Help page on GTIN (Opens in a new tab) and the Google Search Central merchant listing documentation (Opens in a new tab). Google may change these pages, so check the current versions before you rely on a detail.

GTIN, MPN and SKU are not the same thing

Three codes describe a product but come from different owners. A GTIN is assigned by the manufacturer or a numbering body and identifies the product worldwide. An MPN is the manufacturer's own part number. A SKU is the seller's internal stock code. Confusing them leads to wrong values in the wrong fields.

The merchant listing documentation says the MPN property uniquely identifies the product for a given manufacturer. It also asks you to include brand.name when the brand is known, and to include no more than one brand name.

Why a SKU does not belong in the GTIN field

A SKU only has meaning inside your system. Another seller can use the same code for a different knife. Putting it in the GTIN field fills the matching field with a value that matches nothing. The Merchant Center page gives a blunt rule for uncertainty: when in doubt, do not provide a GTIN. Do not guess or make up a value.

Which field gets filled when

• If the manufacturer assigned a GTIN, enter it.
• If the MPN is known, enter it with the GTIN. Merchant Center describes the GTIN as ideally paired with the MPN.
• If the brand is known, enter the brand name.
• Keep the SKU in its own field for your stock tracking.

Valid GTIN formats and the check digit

The Merchant Center page lists the accepted formats. UPC (North America, GTIN-12) has 12 digits, and 8-digit UPC-E codes must be converted to 12 digits. EAN (Europe, GTIN-13) has 13 digits. JAN (Japan, GTIN-13) has 8 or 13 digits. ISBN (books) has 13 digits, and ISBN-10 must be converted to ISBN-13. ITF-14 (multipacks, GTIN-14) has 14 digits.

According to the page, the allowed lengths are 0, 8, 12, 13 or 14 digits. Spaces and dashes are accepted but ignored.

Checking the last digit

The final digit of a GTIN is a check digit and it must be correct. The Merchant Center page points to the GS1 check digit calculator for verification. Practical suggestion: knowing the arithmetic helps you spot a bad number quickly. For a 13-digit number, multiply the first 12 digits alternately by 1 and 3 from the left, add the results, and the check digit is the amount needed to reach the next multiple of ten.

Take 3234567890126, the apparel and food example on the Merchant Center page. The first 12 digits are 323456789012. The products are 3, 6, 3, 12, 5, 18, 7, 24, 9, 0, 1 and 6. They add up to 94, and 6 brings it to 100. The number ends in 6, so the check digit fits. A passing check digit shows only that the number is well formed. It does not show that the number belongs to your knife.

Ranges that are not allowed

Per the page, numbers in restricted ranges starting with 02, 04 or 2 are not allowed, and neither are coupon ranges starting with 05, 98 or 99. In-store barcodes printed for internal use can fall into these ranges. Do not enter them as GTINs.

One GTIN, one product

The page says not to use the same GTIN for multiple products with the same country, language and variant attributes. Each product and each variant carries its own correct GTIN. Duplicated listings break this rule quickly when someone copies a row and forgets to change the number.

Conversions the page asks for

8-digit UPC-E codes become 12 digits and ISBN-10 becomes ISBN-13. If you hold both ISBN formats, include only the 13-digit number. A cutlery catalog rarely meets ISBN, but a cookbook sold next to knives does, and it follows the same rule.

Brand and MPN when a product has no GTIN

Not every product has a GTIN. The Merchant Center page names store-brand or private-label products and customized products as examples. Do not submit a GTIN for them. For store-brand products, submit the brand and the MPN. Leaving out a GTIN that the manufacturer did assign could get the product disapproved.

If you are unsure

The rule on the Merchant Center page is firm: when in doubt, do not provide a GTIN, and do not guess. The page also says that missing or incorrect GTINs may limit visibility. A wrong number is worse than a blank one because it can tie your listing to another product.

A house-brand paring knife

A marketplace seller sells a paring knife under their own label. No manufacturer GTIN exists. The brand field carries the seller's label, and the MPN carries the seller's own product code. If no product code exists, leave the MPN blank rather than invent one.

Identifiers for variants, bundles and multipacks

The Merchant Center page separates two cases for bundles and multipacks. If the manufacturer created the bundle or multipack, submit the GTIN, MPN and brand of the bundle or multipack itself, not those of the individual products. If you created it, submit the GTIN, MPN and brand of the main product for a bundle, or of the individual products for a multipack.

Variants

Each variant carries its own GTIN. The Merchant Center page gives an example of three colors of one t-shirt with three different GTINs. For knives, a blade length or a handle finish that the maker numbers separately follows the same logic. How variants are addressed and canonicalized is a separate topic, linked in the conclusion.

A three-pack of paring knives

If the maker sells a three-pack as one boxed product, the pack has its own GTIN. If you pack three single knives yourself, the page says to use the individual products' identifiers for a multipack you created. State in the listing which case applies, and keep the identifiers consistent with it.

Writing identifiers in markup

The merchant listing documentation counts brand.name, mpn and the GTIN properties among the recommended Product properties. None of them are required; the required Product properties are name, image and offers. A missing identifier therefore does not break the Offer, but filling the recommended properties describes the product better.

The documentation tells you to include all applicable GTIN properties and to prefer the narrowest identifier that applies. A GTIN must be written in numerical form. Practical suggestion: write 3234567890126, not an address on a numbering body's site.

Page and feed must carry the same number

The GTIN in the markup and the GTIN in the feed have to agree. If a feed tool builds one and a template builds the other, confirm that both read the same record. A mismatch here is a silent data problem that shows up later as a rejected item.

Entry rules for marketplace sellers

On a marketplace the seller types the identifiers, and the platform produces the page, markup and feed. A wrong number entered once spreads to all three. Validation belongs at the point of entry.

Give sellers a way out

Offer a "this product has no GTIN" option next to the field. When selected, the form highlights brand and MPN. Sellers who cannot supply a number are then not pushed into inventing one.

Reading duplicates

When a new listing reuses a GTIN that exists elsewhere, ask whether it is the same product listed twice or a copy error. A catalog manager can settle that in a minute; a template cannot.

Cookbooks, accessories and mixed listings

A marketplace that sells knives also sells things that sit beside them: cookbooks, sharpening stones, knife rolls. Each follows its own identifier logic, and a template that treats them all alike will fail on some.

A cookbook sold next to knives

For books and media, the Merchant Center page uses the ISBN-13 as the GTIN value. If you hold both ISBN-10 and ISBN-13, include only the 13-digit number. In markup, the isbn property is valid only on a Book type, and ISBN-13 is the format the documentation prefers. A cookbook page that is typed as Product should use a GTIN property rather than isbn. Practical suggestion: let the template choose the property by product type instead of by a seller-edited field.

Accessories without a GTIN

A hand-made leather knife roll or an engraved block may have no GTIN. Treat them like the house-brand knife: leave the GTIN out, enter the brand, and enter the MPN if you have a product code. Do not borrow the number of a similar commercial product.

Gift sets assembled by the seller

When a seller packs a knife, a board and a cloth into a gift box, the pack is the seller's own creation. According to the Merchant Center page, a bundle you created takes the identifiers of the main product. State clearly in the listing which item is the main product, and keep the other items out of the identifier fields.

Handing the rules to a developer or a seller

Rules that live in a person's head fade. Put them where the work happens: in the seller form and in the template brief.

A brief for the template developer

Say that the GTIN field takes only a verified number of 8, 12, 13 or 14 digits; that the check digit is validated; that a SKU does not go into the field; that products without a GTIN leave it empty and fill brand and MPN; that the brand field holds one name; that each variant and edition carries its own number; and that a bundle uses the identifiers the Merchant Center page assigns to it. Attach the test table as the acceptance test, so the developer can show the six cases passing.

Helper text for sellers

Short sentences beside the form fields do more than a long policy page. For the GTIN field: "Enter the barcode number printed by the maker. If the product has no barcode of its own, tick the box and fill brand and part number." For the brand field: "Enter one brand name, the same one your product page shows." For the MPN field: "Enter the maker's part number, not your stock code."

When a seller disagrees

A seller may insist that a number is right although the check digit fails. Ask for a photo of the packaging or a maker's document. If neither exists, the number stays out. The Merchant Center rule about doubt is clear, and a blank field costs less than a wrong one.

The order for a bulk catalog cleanup

A catalog with hundreds of knives cannot be fixed row by row at random. This order is a practical suggestion.

1. Export every GTIN field.
2. Separate the values whose length is not 0, 8, 12, 13 or 14.
3. Separate the values whose check digit fails.
4. Separate values starting with 02, 04, 2, 05, 98 or 99.
5. List GTINs that appear on more than one product.
6. Verify the flagged numbers against maker documentation or the packaging.
7. Clear the GTIN where verification fails and fill brand and MPN.
8. Decide for bundles and multipacks which product's number applies.
9. Regenerate the feed and the markup from the same record.

The change log

Record the listing address, the old value, the new value and the evidence for each change. The log explains later why a number was removed or replaced. It holds product data only.

Keeping the source of each number

Note where every GTIN came from: packaging photo, maker's product list or supplier sheet. When a number is questioned, the source ends the discussion. This is a practical suggestion.

Worked example: a kitchen knife catalog

A seller lists four knife products on a marketplace. The numbers and names are invented.

A wrong copy and its fix

The seller copied the 20 cm chef's knife row to create the 24 cm listing and left the GTIN unchanged. Two listings now share one number. The fix is to take the 24 cm knife's number from its packaging or the maker's list. If it cannot be found, clearing the field is safer than leaving the wrong number.

Testing before release

Identifier fields can break quietly when a template changes. Keep a small sample of listings and read the output after each change.

If one case fails, assume every listing on the same template is affected, and rerun all six after the fix. Keep the sample stable between releases and store the expected output beside it.

Identifier audit checklist

1. Does the GTIN field hold only a number issued by the maker or a numbering body?
2. Is the length 8, 12, 13 or 14 digits?
3. Is the check digit correct?
4. Does the number start with a restricted or coupon prefix?
5. Is the same GTIN used on another product?
6. Do books use ISBN-13?
7. Does a product without a GTIN have brand and MPN?
8. Is there exactly one brand name?
9. Do bundles and multipacks carry the right product's identifiers?
10. Does each variant carry its own number?
11. Do markup and feed show the same values?

Decision rule: do I enter a GTIN?

Did the maker assign a GTIN, and can you confirm the number from a document or the packaging? If yes, enter it. If not, is the product house-brand or custom-made? If yes, leave the GTIN out and give brand and MPN. If you are unsure, leave it out as well. Guessing a number is not an option.

Mistakes to avoid

A SKU entered as GTIN

The SKU is your internal code. The GTIN is the global number. They do not share a field.

An unchecked check digit

The Merchant Center page requires a correct check digit. A number whose last digit fails is not valid.

One number on several products

Copied listings carry the same number twice. Each product and variant needs its own.

A bundle number mixed with a product number

A maker's pack needs the pack's number; a pack you built needs the main product's or the individual products' numbers.

Two brand names

The documentation asks for no more than one brand name. Pick the one that matches what the page shows.

Frequently Asked Questions

Is a SKU the same as a GTIN?

No. A GTIN is a global product number assigned by the manufacturer or a numbering body. A SKU is your own stock code. Do not enter a SKU in the GTIN field.

What do I enter for a house-brand knife without a GTIN?

Do not submit a GTIN. Merchant Center says to submit the brand and the MPN for store-brand products, and to leave a GTIN out when in doubt.

How long can a GTIN be?

The Merchant Center page lists allowed lengths of 0, 8, 12, 13 or 14 digits. Spaces and dashes are accepted but ignored.

What happens if the check digit is wrong?

The page requires a correct check digit and points to the GS1 calculator. Do not enter a number whose last digit fails.

Which GTIN goes on a knife block set the maker sells as one box?

For a bundle or multipack created by the manufacturer, the page says to submit the GTIN, MPN and brand of the bundle itself, not of the individual knives.

Can I give two brand names, such as the maker and my store?

The merchant listing documentation asks for no more than one brand name in brand.name. Choose the single name that matches what the page shows.

Conclusion

Product identifiers follow a short rule: a GTIN is the maker's verified number, an MPN is the maker's part code, a SKU is your internal code and the brand is a single name. A correct check digit, a valid length and a clean prefix make a GTIN usable. Products without a GTIN go out with brand and MPN, not with an invented number. Bundles, multipacks and variants carry the identifiers of the right product. A bulk cleanup works through lengths, check digits, prefixes and duplicates in order.

For the surrounding feed errors on identifiers, price and stock, read Merchant Center product data errors. For how variants are addressed and marked up, see product variants: URLs, canonicals and structured data. If you want your listings in front of more shoppers, look at the options on the ad spaces page.