Ad glossary
CPM (cost per mille)
The cost of 1,000 ad impressions, used to compare how expensive it is to reach an audience across campaigns and platforms.
CPM stands for cost per mille, where mille is Latin for thousand. It is the amount you pay for 1,000 impressions of your ad. CPM reflects how expensive it is to put your creative in front of an audience, independent of whether anyone clicks or buys.
How to calculate it
CPM = (ad spend ÷ impressions) × 1,000
Worked example (made-up numbers): a campaign spends $600 and delivers 50,000 impressions. CPM = (600 ÷ 50,000) × 1,000 = $12. You can check your own figures with the CPM calculator.
What drives it
On auction-based platforms such as Meta, CPM is shaped by competition for the same audience, so it tends to move with:
- Seasonality: periods like Black Friday and the run-up to Christmas usually bring more advertisers into the auction.
- Audience size and targeting: narrow audiences can cost more to reach than broad ones.
- Placement: feeds, Stories, Reels and other placements are priced differently.
- Ad quality and engagement: ads the platform predicts people will respond to can win auctions more efficiently.
How to read it
A low CPM is not automatically good. Cheap impressions that never turn into clicks or sales are still wasted spend. Most media buyers look at CPM together with CTR, CPC and CPA to understand where costs are coming from: a rising CPA might be an auction problem (CPM went up) or a creative and funnel problem (CTR or conversion rate went down).
Last reviewed Oct 27, 2026