Not to be confused with Impressionism. Claude Monet, Low Tide at Pourville, 1882.

The term is most often used in digital marketing, where an impression counts each time an ad loads and is visible on a website. But impressions aren’t exclusive to digital: they also describe any time a person encounters an out-of-home (OOH) ad, like a roadside billboard. Here’s what makes impressions important.

Generating Business

An ad that reaches far and wide is more likely to bring in new customers than one seen by only a few people. Even though OOH ads don’t usually target a particular audience, OOH reaches consumers more than any other medium.

OOH ads won’t connect with every person who sees them, but they garner far more impressions than most media and reach the most diverse audiences, making it more likely those impressions turn into purchases.

Cost

Advertising costs are often based on impressions, priced per thousand impressions—called cost per mille (CPM). By this measure, billboards and other OOH media are the most efficient ad formats, even including digital.

Tracking Impressions

Digital ads track impressions whenever an ad loads—although bot traffic muddies what counts as a real impression. OOH ads can’t be tracked that way, but alternative approaches offer accurate estimates of how many people were near an ad: