What is CPM?
CPM stands for cost per mille, mille being Latin for a thousand. It is the price an advertiser pays to have an ad shown a thousand times. A $10 CPM means ten dollars buys a thousand impressions; a million impressions cost $10,000. It is the oldest pricing unit in media, inherited from print, where a magazine priced its pages against its circulation, and it is still how television, display, online video, podcasts and out-of-home are bought.
CPM is the price of being seen, not of being noticed. An impression is counted when the ad is served, or on stricter standards when a portion of it is in view for a moment. It makes no promise about attention.
Why it matters
Why CPM matters
CPM is how reach is budgeted and compared. If a brand knows it needs to reach five million people three times, CPM turns that into a number for the finance team. It also lets wildly different media be compared on one scale: a connected TV impression at a $30 CPM against a programmatic banner at $2, and the question becomes what each impression is worth, not what it costs.
For brand advertising, where the goal is memory rather than an immediate click, CPM is the honest unit, because it prices the thing brand advertising actually buys: presence.
It is also where creative quality shows up in the media plan. Two campaigns can pay the same CPM and get very different results, because one film is remembered and the other is skipped. The CPM sets what the attention costs; the work decides whether the attention was worth buying. That is why we brief media and creative together whenever we can, so the format, the length and the placement are chosen for the film rather than after it.
In practice
How CPM works in practice
- 01
A media plan sets the audience and the frequency, estimates impressions, and prices each channel at its CPM to arrive at a budget. Premium placements (a homepage takeover, a live sports broadcast, a Times Square screen) carry high CPMs because the audience is large, attentive or hard to reach elsewhere. Programmatic inventory carries low CPMs because the supply is nearly infinite.
- 02
Once live, the plan is checked against delivered impressions, viewability and audience quality, and the effective CPM (eCPM) is recalculated on what was actually delivered to the right people. The useful discipline is to pair CPM with an outcome metric, such as brand lift or cost per reach point, so the cheapest impressions do not win by default.
Watch out
What people get wrong about CPM
Buying the lowest. A $1 CPM on inventory nobody looks at is more expensive than a $40 CPM in front of the exact audience, because the real price is cost per person who noticed. The other mistake is confusing impressions with people. A thousand impressions might be one person seeing the ad a thousand times; reach and frequency are the numbers underneath CPM, and the plan should be built on them.
