Glossary /
Impression Share
Efficiency & cost
Impression Share
The share of the auction you actually won—a search-ads concept with no direct equivalent on social platforms.
Attribution & Measurement
Unit Economics
Data Governance & Nomenclature
Creative & Delivery
Audiences & Targeting
Mobile & Privacy
Impression share is the percentage of total eligible impressions your ads actually received in an auction-based system. It tells you how much of the available demand you captured versus how much you left on the table.
?
?
What is Impression Share?
Impression share is a Google Ads (and Microsoft Ads) auction metric. For every search where your ad was eligible to appear, the platform tracks whether you actually showed. Divide the impressions you earned by the total you were eligible for, and you get your share of the available auction. It's diagnostic. A low impression share means you're missing auctions you could be winning—usually because of budget or ad rank. Google breaks the gap into lost-to-budget and lost-to-rank, which tells you whether to spend more or improve your ads and bids. It's one of the few ways to size the headroom you have left. Critically, this is an auction-and-eligibility concept. Meta and TikTok don't run keyword auctions where a fixed pool of eligible impressions exists, so they have no direct impression-share equivalent. Treating a social platform's reach or frequency as "impression share" is a category error.
Impression Share formula
Impression Share = Impressions Earned ÷ Total Eligible Impressions
Impression Share = Impressions Earned ÷ Total Eligible Impressions. "Impressions earned" is how many times your ad actually showed; "total eligible impressions" is how many times it could have shown given your targeting, settings, and the auctions you qualified for. The result is the slice of available demand you captured.
Worked example
A Google Ads search campaign in one auction.
Impressions Earned
7,000
Total Eligible Impressions
10,000
Impression Share
70%
7,000 ÷ 10,000 = 70%
Impression share is a Google Ads / Microsoft Ads concept. Meta and TikTok have no direct equivalent.
Impression Share formula
Impression Share = Impressions Earned ÷ Total Eligible Impressions
Impression Share = Impressions Earned ÷ Total Eligible Impressions. "Impressions earned" is how many times your ad actually showed; "total eligible impressions" is how many times it could have shown given your targeting, settings, and the auctions you qualified for. The result is the slice of available demand you captured.
Worked example
A Google Ads search campaign in one auction.
Impressions Earned
7,000
Total Eligible Impressions
10,000
Impression Share
70%
7,000 ÷ 10,000 = 70%
Impression share is a Google Ads / Microsoft Ads concept. Meta and TikTok have no direct equivalent.
How Impression Share differs across ad platforms
Google Ads
Reports impression share natively, plus lost-to-budget and lost-to-rank breakdowns and a top/absolute-top variant for premium positions.
Microsoft Ads
Offers an equivalent impression-share metric on its search network, defined the same way—impressions earned over total eligible.
Amazon Ads
Surfaces auction-share-style metrics (e.g., search-term impression share) on sponsored search, conceptually similar but defined on Amazon's own terms.
Common Impression Share misconceptions
Every ad platform reports impression share.
It's specific to auction-and-eligibility systems like Google Ads and Microsoft Ads. Meta and TikTok have no direct equivalent because they don't expose a fixed pool of eligible impressions per query.
100% impression share is the goal.
Chasing 100% often means overpaying for marginal, low-intent impressions. The right target depends on profitability at the margin, not maxing out the auction.
Related Terms
Frequently Asked Questions
What is Impression Share in simple terms?
Impression share is the percentage of the times your ad could have shown that it actually did show. If you were eligible for an auction 10 times and appeared 7, your impression share is 70%—and the other 30% is demand you missed.
How is Impression Share calculated?
Why does Impression Share differ across ad platforms?
How does Clarisights report on Impression Share?
Attribution & Measurement
Unit Economics
Data Governance & Nomenclature
Creative & Delivery
Audiences & Targeting
Mobile & Privacy
Impression share is the percentage of total eligible impressions your ads actually received in an auction-based system. It tells you how much of the available demand you captured versus how much you left on the table.
?
?
What is Impression Share?
Impression share is a Google Ads (and Microsoft Ads) auction metric. For every search where your ad was eligible to appear, the platform tracks whether you actually showed. Divide the impressions you earned by the total you were eligible for, and you get your share of the available auction. It's diagnostic. A low impression share means you're missing auctions you could be winning—usually because of budget or ad rank. Google breaks the gap into lost-to-budget and lost-to-rank, which tells you whether to spend more or improve your ads and bids. It's one of the few ways to size the headroom you have left. Critically, this is an auction-and-eligibility concept. Meta and TikTok don't run keyword auctions where a fixed pool of eligible impressions exists, so they have no direct impression-share equivalent. Treating a social platform's reach or frequency as "impression share" is a category error.
Impression Share formula
Impression Share = Impressions Earned ÷ Total Eligible Impressions
Impression Share = Impressions Earned ÷ Total Eligible Impressions. "Impressions earned" is how many times your ad actually showed; "total eligible impressions" is how many times it could have shown given your targeting, settings, and the auctions you qualified for. The result is the slice of available demand you captured.
Worked example
A Google Ads search campaign in one auction.
Impressions Earned
7,000
Total Eligible Impressions
10,000
Impression Share
70%
7,000 ÷ 10,000 = 70%
Impression share is a Google Ads / Microsoft Ads concept. Meta and TikTok have no direct equivalent.
How Impression Share differs across ad platforms
Google Ads
Reports impression share natively, plus lost-to-budget and lost-to-rank breakdowns and a top/absolute-top variant for premium positions.
Microsoft Ads
Offers an equivalent impression-share metric on its search network, defined the same way—impressions earned over total eligible.
Amazon Ads
Surfaces auction-share-style metrics (e.g., search-term impression share) on sponsored search, conceptually similar but defined on Amazon's own terms.
Common Impression Share misconceptions
Every ad platform reports impression share.
It's specific to auction-and-eligibility systems like Google Ads and Microsoft Ads. Meta and TikTok have no direct equivalent because they don't expose a fixed pool of eligible impressions per query.
100% impression share is the goal.
Chasing 100% often means overpaying for marginal, low-intent impressions. The right target depends on profitability at the margin, not maxing out the auction.
Related Terms
Frequently Asked Questions
What is Impression Share in simple terms?
Impression share is the percentage of the times your ad could have shown that it actually did show. If you were eligible for an auction 10 times and appeared 7, your impression share is 70%—and the other 30% is demand you missed.
How is Impression Share calculated?
Why does Impression Share differ across ad platforms?
How does Clarisights report on Impression Share?
See Viewable Impression across every channel in one report
See Viewable Impression across every channel in one report
See viewability and vCPM across every platform—display, video, programmatic— in one normalized report, instead of reconciling vendor numbers by hand.
Book a demo