How do you calculate CPM?

Divide the money by the impressions, then multiply by a thousand. A spend of 5,000 across 400,000 impressions is 0.0125 per impression, which is a CPM of 12.50. The page prints that line with your own figures in it, 5,000.00 divided by 400,000 times 1,000, so you can see where the answer came from.

What will a number of impressions cost at a given CPM?

Multiply the impressions by the CPM and divide by a thousand. Set Solving to the money box, enter a CPM of 4 and 50,000 impressions, and the answer is 200.00. The division by a thousand is the step that is easiest to drop: 50,000 impressions at a CPM of 4 is not 200,000, because the 4 buys a thousand impressions at a time.

How many impressions does a budget buy?

Divide the budget by the CPM and multiply by a thousand. A budget of 5,000 at a CPM of 12.50 buys 400,000 impressions. When the division does not land on a whole impression, the page shows the count rounded to one and prints the exact figure underneath, because impressions are only ever delivered in whole ones.

Is this for buying ads or for selling them?

Both, and the Side switch says which. On the buying side the money box is your spend, the money that went to the placement. On the selling side it is your revenue, the money that arrived after the network took its cut, and publisher dashboards usually call the same arithmetic eCPM or RPM. The two are the same identity on different money, so the switch changes every label and never the answer.

What is the difference between CPM and CPC or CPA?

CPM prices a thousand impressions, so it is paid whether or not anyone acts. CPC prices a click and CPA prices an action, and both of those need a response rate before they can be compared with a CPM. This page works the impression arithmetic only: it takes the money, the impressions and the rate you give it, and it makes no claim about what any of them will produce.

What counts as an impression here?

Whatever your ad server counted as delivered. That is not reach, not clicks and not people: the same person seeing an ad five times is five impressions, and a viewability standard may count fewer of them than the delivery report does. The page does the arithmetic on the count you enter and cannot know which definition produced it, which is why the figure is worth checking in the report it came from.

Does it need an account, and is anything sent anywhere?

Neither. The arithmetic runs in the page itself, there is no sign-up and nothing you type leaves your browser. The boxes and the two switches are remembered in your own browser so the page opens where you left it, and clearing your browser data forgets them.

CPM Calculator

CPM is the money divided by impressions, times a thousand, and this page solves that identity in whichever direction you are missing a figure: enter any two of spend, impressions and CPM, and the third one is the answer. The formula is printed with your own numbers inside it, so the arithmetic can be checked rather than trusted, and a figure that will not fit on screen in full, such as a CPM of 4.16666666666667, carries its exact value in a line underneath instead of being quietly rounded. One switch decides whose money it is: buying, where the CPM is what you pay for a thousand impressions, or selling, where it is what you are paid for them and your dashboard probably calls it eCPM or RPM. It runs in your browser, with no account, and nothing you type leaves the page.

CPMReadyEnter any two of spend, impressions and CPM

CPM: -
Spend
Impressions
Solving

Side

Fill in any two boxes and the third is the answer. A k, m or b ending is read, so 400k is 400,000, and the money is in whatever currency you use: the arithmetic is the same in dollars, euros or rupees.

Buying: the CPM is what you pay for a thousand impressions, and the money figure is what left the budget. Impressions are what the ad server counted as delivered, which is not the same as clicks or reach.

Worked examples

Spend 5,000, 400k impressionssolve CPM
CPM 12.50
CPM 12.50, spend 5,000solve impressions
Impressions 400,000
CPM 12.50, 400k impressionssolve spend
Spend 5,000.00

Per thousand, not per impression. The thousand is the whole reason the M is in the name, and it is where the arithmetic usually goes wrong: 5,000 across 400,000 impressions is 0.0125 per impression, which is a CPM of 12.50, not 0.0125 and not 12,500. Going the other way, impressions are the money divided by the CPM and then multiplied by a thousand, so 5,000 at a CPM of 12.50 buys 400,000 of them. Both lines are printed above with your own figures inside them.

What the figures are, and are not. An impression is what the ad server counted as delivered, which is not reach, not clicks and not people. Exact arithmetic: CPM is spend divided by impressions, times one thousand. Enter any two and the third is solved; it computes the stated formula and gives no media-buying advice.

Common questions

How do you calculate CPM?: Divide the money by the impressions, then multiply by a thousand. A spend of 5,000 across 400,000 impressions is 0.0125 per impression, which is a CPM of 12.50. The page prints that line with your own figures in it, 5,000.00 divided by 400,000 times 1,000, so you can see where the answer came from.
What will a number of impressions cost at a given CPM?: Multiply the impressions by the CPM and divide by a thousand. Set Solving to the money box, enter a CPM of 4 and 50,000 impressions, and the answer is 200.00. The division by a thousand is the step that is easiest to drop: 50,000 impressions at a CPM of 4 is not 200,000, because the 4 buys a thousand impressions at a time.
How many impressions does a budget buy?: Divide the budget by the CPM and multiply by a thousand. A budget of 5,000 at a CPM of 12.50 buys 400,000 impressions. When the division does not land on a whole impression, the page shows the count rounded to one and prints the exact figure underneath, because impressions are only ever delivered in whole ones.
Is this for buying ads or for selling them?: Both, and the Side switch says which. On the buying side the money box is your spend, the money that went to the placement. On the selling side it is your revenue, the money that arrived after the network took its cut, and publisher dashboards usually call the same arithmetic eCPM or RPM. The two are the same identity on different money, so the switch changes every label and never the answer.
What is the difference between CPM and CPC or CPA?: CPM prices a thousand impressions, so it is paid whether or not anyone acts. CPC prices a click and CPA prices an action, and both of those need a response rate before they can be compared with a CPM. This page works the impression arithmetic only: it takes the money, the impressions and the rate you give it, and it makes no claim about what any of them will produce.
What counts as an impression here?: Whatever your ad server counted as delivered. That is not reach, not clicks and not people: the same person seeing an ad five times is five impressions, and a viewability standard may count fewer of them than the delivery report does. The page does the arithmetic on the count you enter and cannot know which definition produced it, which is why the figure is worth checking in the report it came from.
Does it need an account, and is anything sent anywhere?: Neither. The arithmetic runs in the page itself, there is no sign-up and nothing you type leaves your browser. The boxes and the two switches are remembered in your own browser so the page opens where you left it, and clearing your browser data forgets them.

Exact arithmetic: CPM is spend divided by impressions, times one thousand. Enter any two and the third is solved; it computes the stated formula and gives no media-buying advice.