CPM Calculator

The whole thing is one ratio

CPM is cost per mille, and mille is a thousand. Everything on this page comes from one relationship rearranged three ways.

CPM = cost ÷ impressions × 1,000
cost = CPM × impressions ÷ 1,000
impressions = cost ÷ CPM × 1,000

The thousand is the only thing that makes it look like more than a division. It exists because a per-impression price would be a string of leading zeros: a $5 CPM is half a cent per view.

Working one out by hand

A $500 spend that delivered 100,000 impressions.

1. Divide the cost by the impressions. 500 ÷ 100,000 = 0.005. That is the cost of one impression, half a cent.
2. Multiply by a thousand. 0.005 × 1,000 = 5, so a $5 CPM.
3. Check it backwards. 5 × 100,000 ÷ 1,000 = 500.

The reverse mode is the useful one when planning. A $1,500 budget at a $6 CPM buys 1,500 ÷ 6 × 1,000 = 250,000 impressions.

What CPM prices, and what it does not

CPM prices impressions. That is its entire scope, and it is worth being exact about, because the number is often quoted as though it described a campaign.

It says nothing about whether anyone looked, clicked, remembered, or bought. Two campaigns can run at an identical CPM and differ completely in every outcome an advertiser cares about, because the impressions were served to different people in different contexts. A lower CPM is a lower price per impression and nothing more; whether it is a better buy depends on facts this calculation cannot see.

This page will not tell you what CPM to aim for. Rates vary by channel, audience, format and season, and any figure printed here as a benchmark would be a number without a source attached to a market it does not know.

Where the delivered figure diverges from the plan

The arithmetic is exact; the inputs are the loose part. The effective CPM you end up paying is usually higher than the one you planned, for reasons that sit outside the division:

• Fees. Ad-server, exchange and agency charges are commonly layered on top of the media cost. If you divide the total invoice by impressions you get a different figure from the rate you were quoted.
• Viewability. A served impression and a viewable one are different counts. Paying a $5 CPM where only 60% were viewable is an effective $8.33 per thousand viewable impressions.
• Frequency. A thousand impressions across 1,000 people and a thousand across 100 people cost the same and are not the same buy.
• Invalid traffic. Filtered impressions may or may not be credited back, and if they are not, they raise the real cost per genuine view.

Edge cases

• Zero impressions. Refused. CPM divides by the impression count, and a campaign that delivered nothing has no cost per thousand rather than an enormous one.
• A zero CPM. Refused in the impressions mode, for the same reason: free impressions would imply an unbounded number of them.
• A zero budget. Accepted. Zero spend buys zero impressions, which is arithmetic rather than an error.
• Fewer than a thousand impressions. Fine. The thousand is a unit of account, not a minimum: 250 impressions at $5 CPM cost $1.25.
• Fractional impressions. The reverse mode can return one, because the division does not know impressions are whole. Round down when planning; a fraction of a view is not deliverable.

Comparing a CPM buy against a CPC one

The two are only comparable through a click-through rate. At a $5 CPM, a thousand impressions cost $5; if 1% of them are clicked, those ten clicks cost 50 cents each. At a 0.1% rate the same thousand yields one click at $5.

So a CPM buy is a bet on the click-through rate holding up, and a CPC buy moves that risk to the seller. Which is cheaper is not a property of either rate; it is a property of the rate you actually achieve, and this page cannot predict it.

Your figures stay in this page

The cost, impressions and CPM you enter are computed by this page in your browser. Nothing is sent to a server, nothing is stored after you close the tab, and there is no account.