Glossary

Cost per mille (CPM)

The price an advertiser pays for one thousand ad impressions, regardless of clicks or conversions.

Also called: CPM, cost per thousand impressions

Cost per mille, from the Latin for thousand, is the price of one thousand ad impressions, calculated as CPM = (ad spend / impressions) * 1000. It is a pricing and measurement unit used mainly for display, video, and other formats bought to build exposure rather than to drive an immediate click, and it says nothing about whether anyone engaged with or even saw the ad.

CPM differs from cost per click and cost per acquisition in that it charges for delivery of the ad rather than for a user action, which shifts the performance risk onto the advertiser: a campaign can hit its CPM target while generating almost no clicks. Because raw impression counts can include ads that were technically served but never actually on-screen, CPM is increasingly reported alongside ad viewability as "viewable CPM," which prices only impressions that met a viewability standard.

CPM is the standard metric for planning and comparing the cost of reach and brand campaigns, and it feeds directly into reach and frequency planning. A low CPM is not automatically good value if the inventory is low quality, poorly targeted, or affected by invalid traffic.

Last reviewed September 22, 2026

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Related terms

Impression One instance of an ad being served and rendered on a page or app, whether or not anyone noticed or clicked it. Cost per click (CPC) The amount an advertiser pays, on average, each time a user clicks on a paid ad. Cost per acquisition (CPA) The average amount spent on advertising to generate one conversion, such as a sale, lead, or signup. Reach and frequency Reach is how many unique people saw an ad; frequency is how many times, on average, each of them saw it. Ad viewability A measure of whether an ad impression had the actual opportunity to be seen, based on standardized on-screen thresholds.