An item ID is the unique code you assign to each product in your product feed, so Google can tell one item from every other item you sell. In the feed it is the id attribute, and Google’s interfaces sometimes call it the offer ID or product ID. Every size or colour sold as a separate variant needs its own item ID.
How item IDs work
When you submit products to Google Merchant Center, each row in the feed must carry an ID that no other product in the same account uses. You choose the format; many shops use their SKU from the ecommerce platform, such as TSHIRT-NAVY-M. Google sets a character limit, and the ID should only use plain letters, numbers and simple punctuation.
Google uses the item ID to recognise the same product across feed updates. If the ID is unchanged, a price change or new image updates the existing product and keeps its performance history. If the ID changes, Google treats it as a brand-new product and the old one disappears, along with its click and conversion data.
The ID also links your feed to the rest of Google Ads. Shopping and Performance Max reports can be broken down by item ID, product groups can be split on it, and dynamic remarketing uses it to show people the exact product they viewed. For that to work, the product ID your website tag sends must match the item ID in the feed character for character.
Why it matters
For a UK online shop, item IDs are the backbone of Shopping ads reporting. Stable IDs let you see which products earn their spend over months, decide which to push in the run-up to Black Friday or Christmas, and spot products that cost money without selling.
Unstable IDs cause quiet damage. A platform migration, a plugin update or a feed app that regenerates IDs can reset the history of every product at once, so automated bidding starts again from nothing. A typical case is a shop whose best sellers vanish from reports overnight, simply because a new feed tool used a different ID format from the old one.
Common mistakes
- Changing the ID format when moving platform or feed app, which resets every product’s history.
- Giving all variants of a product the same ID, so sizes or colours overwrite each other.
- Reusing an old ID for a completely different product, which carries over history that no longer applies.
- Mismatched IDs between the feed and the remarketing tag, so dynamic ads cannot find the product.
- Including spaces or unusual characters that cause the row to be rejected.
How to act on it
Decide on one ID scheme, usually your platform’s SKU or variant ID, and document it. Before any platform change or new feed tool goes live, export the current feed and check that the new one produces identical IDs for the same products. If it cannot, map old IDs to new ones and accept a temporary dip in bidding performance rather than discovering it later.
Check that each product variant has its own ID and shares an item group ID with its siblings. Then compare the IDs in your remarketing tag with the feed. Feed checks of this kind come before any campaign build in my Performance Max management work, because every product decision in the campaign depends on them.