Formula
CPM = spend / impressions × 1,000
Why it matters
It shows how expensive an audience is to reach. A low CPM is not always better, since cheap impressions can reach people who never convert.
Glossary // C / Media buying
What is Cost per mille (CPM)?
Definition
Cost per mille is the price paid for one thousand ad impressions, calculated as spend divided by impressions times 1,000.