Impression

An impression is counted each time an ad is shown. If 1,000 people each see an ad once, that is 1,000 impressions. It measures exposure, not action.

Impressions matter on both sides of search arbitrage. On the buying side, many platforms price by the thousand impressions (CPM), so the buyer pays for the ad to be seen and the CTR decides how many clicks that buys. On the selling side, the feed counts impressions of search ads on the publisher's page. Search ads normally pay per click, so an impression with no click earns nothing, but feed reports still show impressions and derive figures such as RPM and Ad CTR from them.

Impression counts also serve as an activity test. Google states that, as of 20 August 2025, an AdSense for Search publisher must record at least 20 search ad impressions in at least two of the previous six months to keep access to the product.

Showing ads that nobody can really see, for example hidden or stacked on top of each other, creates fake impressions and is a form of ad fraud (hidden ads).

An example

For example, an ad shown 20,000 times at a $5 CPM costs $100. If 1% of viewers click, that is 200 clicks at an effective $0.50 each.