Written by Krisztián Stark
Key takeaways
- CPM = ad spend divided by impressions, times 1,000. It is the price of 1,000 ad views, whether anyone reacts or not.
- CPM is what an advertiser pays. eCPM and RPM are usually what a publisher earns, so do not compare them directly.
- Buy CPM when being seen is the goal, check that impressions were viewable, and judge the campaign by what the views led to.
What is CPM (cost per mille)?
CPM, or cost per mille, is the price an advertiser pays for 1,000 impressions of an ad. “Mille” is Latin for thousand, which is why CPM is also read as cost per thousand. You pay for the ad being shown, whether or not anyone clicks or acts.
An impression is one display of an ad. Pricing per thousand keeps the numbers readable: a $5.00 CPM is easier to work with than half a cent per view.
The CPM formula
CPM = ad spend ÷ impressions × 1,000.
If you spend $60 and get 20,000 impressions, your CPM is $60 ÷ 20,000 × 1,000 = $3.00.
The same formula works backwards for planning: impressions = budget ÷ CPM × 1,000.
Quick math: how far does $200 go?
At an $8.00 CPM, a $200 budget buys $200 ÷ $8.00 × 1,000 = 25,000 impressions. If you want each person to see the ad about three times, that is roughly 8,300 people reached. At a $4.00 CPM, the same budget doubles both numbers. The prices are illustrative, not benchmarks.
CPM vs eCPM vs RPM
All three are “per thousand” numbers, but they answer different questions, and mixing them up is one of the most common reporting mistakes.
| Term | Who uses it | What it measures |
|---|---|---|
| CPM | Advertisers | What you pay per 1,000 impressions |
| eCPM, effective CPM | Mostly publishers, sometimes advertisers | Earnings or cost per 1,000 impressions, worked out from any pricing model |
| RPM, revenue per mille | Publishers | Earnings per 1,000 page views or impressions |
The “effective” in eCPM matters: it lets you express a campaign bought per click or per action as if it were bought per thousand impressions, so different deals can be compared. What a publisher earns per 1,000 impressions is also lower than what advertisers pay for them, because the ad platform in between keeps a share. Page RPM is different again: a page with three ads earns from three impressions per view. For the publisher side, read eCPM vs RPM and eCPM and EPC explained.
Viewability: is every impression really seen?
An ad can be “served” at the bottom of a page nobody scrolls to, or in a tab that is never opened. That still counts as an impression in many reports. Viewability measures whether the ad actually had a chance to be seen.
Google’s Active View documentation summarizes the industry standard developed by the Media Rating Council (MRC):
- A display ad is viewable when at least 50% of its area is on screen for at least one second.
- For large display ads of 242,500 pixels or more, at least 30% of the area for at least one second.
- A video ad is viewable when at least 50% of its area is on screen while it plays for at least two seconds.
Some platforms let you buy viewable impressions only, often called vCPM. Even when you buy standard CPM, check the viewability rate in your reports. A cheap CPM with low viewability can cost more per viewable impression than a pricier one.
Illustrative example: the cost of what was actually seen
Placement A costs $2.00 CPM with 40% viewability, so each 1,000 viewable impressions costs $2.00 ÷ 0.40 = $5.00. Placement B costs $3.00 CPM with 75% viewability, which is $4.00 per 1,000 viewable impressions. The pricier placement is the better buy. The rates are made up for the arithmetic.
When CPM is the right model
CPM buys attention, so it fits goals where being seen is the point:
- Brand awareness, when you want people to recognize your name before they need you.
- Launches and announcements, where reach in a short time matters more than clicks.
- Retargeting, reminding people who already visited you, where a view alone can bring them back.
- Video, where the message lands even when nobody clicks.
For awareness, the numbers to watch are reach (how many different people saw the ad), frequency (how often each saw it), and viewability. Too low a frequency and nobody remembers you, too high and you pay to annoy the same people.
CPM fits less well when you need a specific action. Then turn the CPM into a cost per result: CPM ÷ (1,000 × click rate × conversion rate), and compare it with what that result is worth. CPM vs CPC vs CPA walks through that comparison, and What is CPC? shows how CPM and CTR combine into a click price.
Common CPM mistakes
- Chasing the lowest CPM. Very cheap impressions often sit in poor placements, below the fold, or in front of bots.
- Ignoring viewability and fraud. Impressions are easy to fake. See Ad fraud and bot traffic for warning signs.
- Comparing CPMs across formats. A video impression, a banner, and a social post are not the same exposure.
- Treating CPM as a publisher’s earnings. What a site earns per 1,000 impressions is lower than what advertisers pay for them.
- No measure of effect. Track branded searches, direct visits, or a simple survey, so you know the views did something.
When you want results, not impressions
Sharklio does not sell impressions. If your awareness goal can be expressed as an action, such as following your social account, joining your community, or subscribing to your newsletter, a task campaign lets you pay only for the completions you approve, at a price you set for each country, from $0.01. Multi-step offer campaigns, available by arrangement with our team, pay per step your server reports through a postback. You can create a free account and your first campaign today, and run it next to your CPM campaigns to compare the cost of a real result.
Frequently asked questions
What does CPM stand for?
Cost per mille, meaning cost per thousand. It is the price of 1,000 ad impressions.
How do you calculate CPM?
Divide your ad spend by the number of impressions and multiply by 1,000. $45 for 15,000 impressions is a $3.00 CPM.
Why is it called CPM and not CPT?
The M comes from “mille”, Latin for thousand, as in the Roman numeral M. Some media still say cost per thousand, but CPM is the standard abbreviation in digital advertising.
What is the difference between CPM and eCPM?
CPM is a price agreed per 1,000 impressions. eCPM is calculated after the fact, by dividing total earnings or cost by impressions and multiplying by 1,000, so campaigns bought on any model can be compared.
What is a good CPM?
One that delivers viewable impressions to the right audience at a cost your goal can justify. CPMs vary widely by country, format, audience, and season, so compare against your own past campaigns rather than a general average.
Is CPM or CPC better?
CPM fits awareness, where being seen is the goal. CPC fits traffic, where you want visits. If you need a specific action, consider paying per action instead.
