CPM (Cost Per Mille)

CPM (cost per mille) is the price an advertiser pays for one thousand ad impressions, where "mille" is Latin for thousand. It is calculated as CPM = (total spend ÷ impressions) × 1,000. With a $5 CPM, every 1,000 times the ad is served costs $5, whether or not anyone clicks.

CPM is the default pricing model for awareness and reach campaigns, and the underlying currency of most programmatic auctions. Display, video, and many native buys clear on a CPM basis even when the advertiser ultimately cares about clicks or conversions, the network simply translates other goals back into an effective CPM to rank bids.

Why it matters#

Because you pay for exposure rather than action, CPM rewards efficient delivery to the right audience. Two factors quietly inflate its true cost: how many impressions are actually seen versus served, and how engaged that audience is. An impression that is paid for but never enters the viewport wastes budget, which is why buyers pair CPM with Viewability metrics. The count itself is defined by the Ad Impression.

CPM is the buy-side mirror of a publisher's earnings metric, RPM (Revenue Per Mille), what one side pays per thousand, the other earns per thousand. It contrasts with CPC (Cost Per Click), which charges only on clicks; a high-CTR ad on a CPM buy effectively lowers your cost per visitor even though the impression price is fixed.

Related terms: CPC (Cost Per Click), Ad Impression, Viewability, and RPM (Revenue Per Mille).