What is CPM?
CPM, cost per mille, is what you pay for one thousand ad impressions. Mille is Latin for thousand. It is the standard pricing unit for awareness and reach campaigns, where you are billed for being seen rather than clicked.
CPM measures buying cost, not performance. A low CPM is cheap reach; whether it is good reach depends on who sees the ad.
The CPM formula.
CPM = (total ad spend divided by impressions) times 1,000. To plan a budget the other way, spend equals CPM divided by 1,000, times your target impressions.
Keep spend and impressions over the same campaign and window. CPM drifts if you mix a week of spend with a month of delivery.
A worked example.
You spend 5,000 dollars for 1,000,000 impressions. CPM is 5,000 divided by 1,000,000, times 1,000, which is 5 dollars. To buy 2,000,000 impressions at that CPM, you would budget 10,000 dollars.
What is a good CPM?
Benchmarks vary widely by platform and targeting, so there is no single number. Broad, untargeted reach is cheap per thousand; narrow, high-intent audiences cost more but can be worth it. A higher CPM against the right audience often beats cheap impressions wasted on the wrong one.
CPM only becomes a performance metric when you pair it with CTR and CPC, which turn impressions into clicks and clicks into cost.
How to lower your CPM.
Broaden targeting, improve ad relevance, and test placements, since platforms price more relevant ads lower. But cheaper impressions are not the goal if they reach the wrong people.
Organic reach carries no CPM at all. Content that ranks earns impressions every month without a media buy, which lowers your blended cost of reach over time. See how we build durable B2B SaaS reach through SEO.