Variant Feeds in Google Merchant Center: item_group_id, Size, Color, and GTIN

Variant feeds fail when the relationship between products is unclear. Google needs to understand which items belong to the same parent product while receiving a unique identity, price, availability, and landing page for each offer.

The variant model

• ID: stable identifier for the individual variant.
• item_group_id: shared identifier for variants of the same parent.
• Attributes: size, color, material, or other distinguishing values.
• Identifiers: GTIN, brand, and MPN when genuine.
• Offer values: price, availability, image, and link for that variant.

Audit relationships before attributes

Group the feed by item_group_id and check whether each group represents one real product. Then verify that variant IDs are unique and stable across updates.

Handle size, color, and GTIN carefully

Use the values customers see on the page. A manufacturer-assigned GTIN belongs to the variant where applicable. If a product genuinely has no identifier, follow Google’s identifier guidance rather than inventing a barcode.

The five-variant test

1. Pick five parent products with multiple variants.
2. Export every variant ID and item_group_id.
3. Open each exact variant link.
4. Compare size, color, price, availability, image, and GTIN.
5. Check the issue status after processing.

Compare this audit with the variant management guide and duplicate GTIN audit.

Source: Google Merchant Center product data specification