impression share

IS is reported per network. Search impr. share covers the Search Network and Display impr. share covers Display. Google also reports absolute top impr. share (ATIS): the impressions your ads got in the absolute top slot (the first ad above the organic results) divided by the impressions they were eligible to get in that slot. ATIS is a Search metric and is also available for Shopping and Performance Max. Eligible impressions are Google’s own estimate, based on your targeting, approval status, and quality, of every auction you could realistically have entered.

Where the lost share goes

Google splits the gap into two buckets. Search lost IS (budget) is the share of eligible auctions you missed because the campaign ran out of budget. Search lost IS (rank) is what you lost to weak Ad Rank. Ad Rank is set by your bid, your ad and landing-page quality, the Ad Rank thresholds, the competitiveness of the auction, and the context of the search, not by bid alone. The split tells you which lever to pull: add budget, or fix relevance and landing-page quality.

Example: if Search IS is 62%, lost IS (rank) is 30%, and lost IS (budget) is 8%, most of your missing reach is a quality problem, not a spend problem. Pouring in more budget barely moves it.

There is no true impression-share metric in organic search. Search Console reports raw impressions and average position, but Google publishes no “total eligible” denominator for organic, so you cannot compute a clean percentage. The organic analog is SERP visibility, or share of voice: how often your pages surface for queries you could rank for.