What is impression share?
Impression share is the share of the impressions your ads were eligible for that they actually received, which shows how much of the available demand you are reaching.
Formula
Impression share = impressions received ÷ estimated eligible impressions × 100
Worked example, not a result
Reading headroom before adding budget
Say a campaign was eligible for an estimated 70,000 impressions in a month and received 27,300 of them. Impression share is 39 percent, so the campaign missed most of the times it could have appeared.
That sounds like a problem and it is really an opportunity, provided the campaign is already profitable. Roughly six in ten of the moments when someone searched and your product could have appeared, it did not. If the orders you are getting already pay for themselves comfortably, there is a queue of unserved demand sitting there.
The next question is why the share is low, and there are only two answers worth having: the budget ran out, or the ads were not competitive enough to be chosen. The platform reports both separately, and each one has a different fix. Raising budget on an account losing share to rank does nothing at all.
The eligible and received counts here are made up.
Why it matters
Impression share is the honest measure of headroom on the visitors lever. Revenue growth from paid search is capped by how often you can appear, and this is the only metric that tells you how far you are from that cap without guessing.
It also settles a common argument. When results plateau, the question is always whether the market is saturated or the account is under invested. A high share says you are near the ceiling for those searches and growth has to come from new products, new terms or the other three levers. A low share says the demand is there and something in the account is stopping you reaching it.
For a store owner it turns budget decisions into evidence. Adding spend to a campaign already taking most of the available impressions pushes money into worse auctions. Adding it to a profitable campaign at a low share, held back by budget, buys demand that already exists.
Common mistakes
- Treating a high share as an achievement. Taking nearly every impression on a narrow, low value set of searches is not the same as reaching the market.
- Adding budget without checking why share is low. If the shortfall is competitiveness rather than budget, the extra money sits unspent and confidence in the account drops for no reason.
- Reading it across a whole account. Share varies enormously by product and by search term, and the account level figure averages a starved campaign with a saturated one.
- Forgetting that the eligible number is an estimate. It is useful for direction and trend, not a precise count to make fine decisions against.
Related terms and answers
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