CPM definition: what cost per mille means

CPM meaning, in one line

CPM stands for cost per mille, where “mille” is Latin for thousand, and it is the cost of 1,000 impressions. Google Ads describes CPM bidding as a way to pay per thousand views (impressions) on the Display Network,^[1] and Meta reports CPM as the average cost for 1,000 impressions: amount spent ÷ impressions × 1,000.^[2]

Because the number is normalised to 1,000, CPM lets you compare a $300 test with a $30,000 campaign, or a newsletter sponsorship with a video placement. To work out a real campaign, use the CPM calculator.

How CPM ads are bought

CPM ads are bought per thousand impressions, so the advertiser pays for the ad being shown whether or not anyone clicks. That suits awareness goals, where the job is to put a message in front of as many of the right people as possible. In an auction, the CPM you bid is a maximum; the price you actually pay depends on competition for the same audience. On a direct deal, the CPM is a fixed rate card price.

Platforms that charge per click or per conversion still report a CPM, because it is just spend divided by impressions. That reported figure is an effective CPM (eCPM): what the impressions ended up costing, whatever the billing model.

CPM vs vCPM, eCPM, RPM, CPC and CPA

Viewable CPM counts only impressions that met a viewability standard. The IAB/MRC guideline treats a display ad as viewable when at least 50% of its pixels are on screen for at least one second, and a video ad when 50% is in view for two seconds.^[4] Google Ads’ vCPM bidding charges only for those viewable impressions.^[1]

RPM is the publisher’s side of the same market. YouTube defines CPM as the cost per 1,000 ad impressions before YouTube’s revenue share, and RPM as a creator’s total revenue per 1,000 views after the share.^[5] The two will never match: not every view shows an ad, and the platform keeps a share.

Worked example: eCPM of a CPC campaign

A search campaign pays $1.20 per click and gets a 0.8% clickthrough rate. Every 1,000 impressions produce 8 clicks, which cost $9.60, so its effective CPM is $9.60 even though nothing was bought per thousand. Going the other way, CPC = CPM ÷ (1,000 × CTR); the CPC calculator does that conversion for any pair of numbers. The CTR formula explains where the 0.8% comes from.

Is a high CPM bad?

A high CPM is not bad on its own; it is bad only when the results bought with it cost more than they are worth. Audiences that are valuable to many advertisers (high-income, in-market or business buyers) cost more per thousand. Expensive impressions that convert can beat cheap ones that do not, so compare campaigns on cost per result. Textbook marketing metrics treat impressions and CPM as reach measures and conversions and ROAS as outcome measures for that reason.^[6] To see whether the outcomes pay, use the ROAS calculator.

Where CPM goes wrong

1. Treating impressions as people. An impression is a showing, not a viewer. Meta counts the times ads were on screen,^[3] so one person can produce many. People reached is a separate metric; the impression calculator estimates it from frequency.
2. Comparing a vCPM with a CPM. A viewable-only price per thousand will look higher than a served-impression price for the same inventory.
3. Reading CPM as a performance metric. CPM tells you what attention cost, not what it achieved. Pair it with CTR and conversion rate.

CPM, CTR and CPC are linked: if you know any two, the third follows. CPM = CPC × CTR × 1,000, so a $0.50 CPC at a 2% CTR is a $10 CPM.

Not affiliated with Google, Meta, YouTube or the IAB. Platform names are trademarks of their owners and appear only to identify whose documentation we cite.