A manufacturer part number (MPN) is the code a manufacturer gives a specific product to tell it apart from everything else it makes. In a Google product feed, the mpn attribute carries that code, and together with the brand it identifies exactly what you are selling when the product has no barcode number.
How MPNs work in product feeds
Google identifies products through unique product identifiers. The main one is the GTIN, the number under the barcode, which in the UK is usually a 13-digit EAN. The rules in Google’s product data specification work roughly like this:
- If the product has a GTIN, submit it with the brand. The MPN is then optional, though still useful.
- If it has no GTIN, submit the brand and the MPN together.
- If it has neither, as with handmade, made-to-order or vintage items, set identifier_exists to “no” so Google does not expect one.
The MPN belongs to the manufacturer, not the retailer. A shop stocking a branded radiator valve should use the part number printed on the box or listed in the maker’s trade catalogue, not its own stock code, which goes in the item ID attribute. If you make the product yourself, your own part numbers are the MPN, because you are the manufacturer.
MPNs have no fixed format. They can mix letters, numbers, dashes and full stops, and Google expects them exactly as the manufacturer writes them, up to 70 characters. Copy them from a data source rather than retyping them, because a single dropped character turns a valid code into a different product or into nothing at all.
Why it matters
Identifiers help Google understand which product you are offering and group your listing with other offers of the same item. That affects whether and where it shows in Shopping ads, free listings and product comparisons. Products missing identifiers they should have can show less often and may be flagged in Merchant Center.
For UK retailers selling spare parts, components and trade supplies, MPNs matter even more, because buyers search with them. Someone hunting for a replacement filter or a specific spare part often types the part number straight into Google. A product with the correct MPN in its feed and on its page stands a far better chance of appearing for that exact search.
Common mistakes
- Putting your own SKU or stock code in the mpn field, which tells Google something false about the product.
- Submitting an MPN without a brand, or with a brand that does not match the manufacturer.
- Making up MPNs to clear a warning. Wrong identifiers can get products matched to the wrong item or disapproved.
- Setting identifier_exists to “no” on branded products that do have identifiers, just to stop the warnings.
- Using one MPN for every size or colour when the manufacturer gives each variant its own code.
How to act on it
Open the diagnostics in Merchant Center and filter for issues about missing or incorrect identifiers. Then take MPNs from the source, such as supplier price lists, manufacturer data sheets or your supplier’s product data file, rather than typing them by hand. Map them into the feed through your ecommerce platform or feed tool, check the brand values match, and keep identifier_exists for products that genuinely have no identifiers.
Show the MPN on the product page as well, both to shoppers and in the page’s product structured data, so it can be found for part number searches in organic results too. Feed quality, identifiers included, is the groundwork I check before any shopping activity in Performance Max campaigns.