Impression

What Is an Impression?

In digital advertising, an impression is one instance of an advertisement being displayed to a user. Each time a banner loads on a web page, a sponsored post appears in a mobile app feed, or a video ad starts playing, the publisher or platform records one impression. Impressions are among the most common metrics used to describe how widely an ad campaign has been seen, and they serve as a standard unit for pricing many types of online ads.

How Impressions Are Counted

Impressions are typically logged by an ad server, which delivers the ad to a page and records when that delivery happens. Because the same person may see an ad several times, impressions do not equal unique viewers. Marketers track repeat exposure separately as reach and frequency.

Not every delivered ad is actually seen. Industry bodies have defined viewability standards that require a minimum portion of an ad's area to be on screen for a minimum length of time before it counts as a viewable impression. Some traffic is also generated by automated bots, which advertisers and auditors try to filter out.

Impressions in Pricing and Investing

Many online ads are sold on a cost-per-thousand-impressions basis, known as cost per mille (CPM). Under this model, the advertiser pays a set rate for every thousand impressions served. Companies that depend on advertising, such as search engines, social networks and publishers, often report impression counts in their earnings materials. Investors may look at impression trends alongside average revenue per user to judge advertising demand.

Impression counts alone have limits. Revenue depends on the price per impression and how much advertising space is actually sold, so a rise in impressions does not guarantee higher income. Changes in the mix of ad formats, or in how a company defines and counts impressions, can also make comparisons between periods or companies difficult.