What is CPM (Cost per 1,000 impressions)?

CPM, or cost per 1,000 impressions, is the average price of 1,000 ad impressions. Meta calculates it as amount spent divided by impressions, multiplied by 1,000. The M comes from mille, Latin for thousand. On Meta, CPM is the price of the exposure an ad set won in the ad auction, and it says nothing on its own about what that exposure produced.

Meta warns that when an ad set optimises for conversions, CPM may not be a good guide to performance, because the delivery system may buy more expensive impressions when they lead to cheaper conversions. Read it next to cost per result.