Ad Impression Share shows the percentage of impressions that a Google Ad receives compared to the total number of eligible impressions
Ad Impression Share is a metric that quantifies the percentage of impressions that an advertiser’s ad receives compared to the total number of eligible impressions.
It’s a representation of the advert’s visibility within a particular market or for specific keywords. A higher impression share indicates that the ad is being shown frequently to users searching for the relevant terms.
For example, if a campaign has an impression share of 80%, it means that the ad is being displayed 80% of the time when it is eligible to be shown. The remaining 20% represents missed opportunities where the ad wasn’t displayed due to various factors.
The formula to calculate Ad Impression Share is straightforward:

By applying this formula, advertisers can obtain the percentage of times their ad was shown in relation to the potential times it could have been shown.
Several factors impact an ad’s impression share: