Definition: CPM, or cost per mille, is the price an advertiser pays for 1,000 impressions of an ad, used both as a way to buy ads and as a metric for comparing campaign costs.
Also called: cost per thousand impressions, cost per mille
Updated October 11, 2026
CPM = ad spend ÷ impressions × 1,000CPM has two meanings. As a bidding model, you pay for impressions whether or not anyone clicks; Google Ads describes CPM bidding as paying per one thousand views (impressions), per its help centre. As a metric, CPM is calculated for any campaign, even one bought per click, so you can compare how expensive it was to reach people across platforms and audiences.
CPM is the right lens for awareness campaigns, where the goal is to be seen. For traffic or sales, a low CPM is not enough on its own: cheap impressions that nobody clicks cost more per result than pricier impressions that convert.
A campaign spends $600 and earns 150,000 impressions. CPM = 600 ÷ 150,000 × 1,000 = $4.00.
Impressions are the total number of times a post was displayed on screen, counting repeat views by the same person.
Cost per click (CPC) is the amount an advertiser pays for each click on an ad, either as the price set in a pay-per-click auction or as total spend divided by clicks.
Reach is the number of unique people who saw a post or account at least once in a given period.
A dark post is a sponsored post that is shown only to the audience an advertiser targets and never appears as a regular post on the brand’s own page or profile.
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