CPM (cost per thousand impressions)
Also known as: Cost per mille, Average CPM
In short
The advertising cost associated with 1,000 impressions, calculated by dividing spend by impressions and multiplying by 1,000.
Calculate the cost of delivery
CPM expresses advertising cost relative to the number of impressions delivered. For a reporting period, calculate it as ad spend ÷ impressions × 1,000. Use spend and impressions from the same campaign scope, currency and date range.
An impression is a recorded ad display, not a unique person. One person can generate several impressions. A viewable-impression measure uses a different denominator, so CPM and viewable CPM are not interchangeable.
CPM can describe a buying model or a calculated reporting metric. Seeing CPM in a report does not by itself tell you how the campaign was billed.
Illustrative calculation
Imagine a fictional campaign spending $240 for 60,000 impressions during one week. Its CPM is $240 ÷ 60,000 × 1,000 = $4.
Another campaign spends $60 for 10,000 impressions. The combined CPM is $300 ÷ 70,000 × 1,000, or about $4.29. Averaging the two campaign CPMs would give the wrong combined result because the impression volumes differ.
Interpret the audience and outcome
A lower CPM means cheaper measured impressions within that comparison. It does not establish better customer reach, more conversions or higher profit. Compare placements and audiences alongside frequency, response and the relevant business outcome. An undefined or zero-impression denominator cannot produce a meaningful CPM.