CPM Calculator

Enter any two of total cost, impressions and CPM, and this gives the third. The useful part comes after that: add your reach and it works out how many real people you got in front of, add viewability and it prices the impressions nobody saw, add a click rate and it turns the whole thing into a cost per click.

Enter any two. Leave blank whichever one you want worked out.

Optional, and this is where it gets useful. Any of these you know will be worked into the answer.

Unique people, not impressions.
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The formula

CPM = total cost ÷ impressions × 1,000

That is the whole of it, and it is why most CPM calculators are one line of arithmetic in a box. The M is the Roman numeral for a thousand, from mille, so CPM is cost per thousand and never cost per million. $500 across 250,000 impressions is a $2.00 CPM.

The rest of this page is about the three things that division cannot tell you.

One: impressions are not people

This is the misreading that costs the most money. An impression is one ad served once. It is not a person, and the gap between the two is frequency.

frequency = impressions ÷ people reached

Consider two campaigns that both buy 1,000,000 impressions at a $5.00 CPM, for $5,000 each:

Campaign ACampaign B
Impressions1,000,0001,000,000
CPM$5.00$5.00
People reached500,000100,000
Frequency2.010.0
Cost per 1,000 people$10.00$50.00

Identical CPM. Identical spend. One reached five times as many humans as the other, and cost a fifth as much per person to do it. The CPM is the same number in both columns and it is useless for telling them apart.

Neither is automatically wrong. If you need someone to remember a brand name, a frequency of ten may be the point. If you are announcing a sale that ends on Sunday, showing it to the same hundred thousand people ten times is mostly annoyance. But you cannot make that judgement from a CPM, and a CPM is usually all anyone quotes.

Two: some of those impressions were never seen

An ad that loads below the fold and never scrolls into view was still served, still counted, and still billed. The Media Rating Council's standard for a viewable display impression is at least 50% of the ad's pixels in view for at least one continuous second, and two seconds for video.

So a campaign running at 60% viewability spent 40% of its money on impressions that had no chance of doing anything:

ViewabilityEffective CPM on a $5.00 buyUplift
100%$5.001.00x
70%$7.141.43x
60%$8.331.67x
50%$10.002.00x

A $5.00 CPM at 50% viewability is a $10.00 CPM with extra steps. This is worth checking before concluding that one publisher is cheaper than another, because cheap inventory and poor viewability tend to arrive together.

Three: what a click and a customer actually cost

Every CPM buy has a cost per click hiding inside it. The click rate is what sets it:

CPC = CPM ÷ 1,000 ÷ click rate

A $10.00 CPM at a 0.5% click rate is a $2.00 cost per click. At 0.25% it is $4.00. Halving the click rate doubles the price of a click without the CPM moving at all, which is why creative quality shows up in the media bill.

Carry it one step further and you reach the only number anyone outside marketing asks about. At a 3% conversion rate, those $2.00 clicks become $66.67 customers. Whether that is good depends on what a customer is worth, which is what the lifetime value calculator is for, and the cost per acquisition calculator works out the ceiling you can afford to pay.

CPM and RPM are the same money from opposite ends

These get confused constantly, and they are not two names for one thing:

They differ for two reasons at once. The platform keeps a share of what the advertiser pays, and one pageview can carry three or four ad units, so the two figures are not even counting the same events. A publisher with a $3.00 RPM and an advertiser paying a $5.00 CPM can be looking at exactly the same ad slot. If you are on the receiving end of this, the AdSense calculator works from published per category rates and handles the publisher side.

What a CPM is worth as a comparison

A CPM is a price. It is not a result, and it is only comparable between two placements when the audience, the format, the position on the page and the viewability are all alike. They usually are not.

Broad display inventory often runs $1 to $5. Social sits in the mid single digits. Tightly targeted professional audiences, connected TV and podcast reads can run $20 to $50 and be entirely reasonable buys, because the person on the other end is worth more. The cheapest CPM you can find is almost always cheap for a reason.

Judge a campaign on what a customer cost, not on what a thousand impressions cost. The return on ad spend calculator closes that loop.

Frequently asked questions

What is CPM and how do you calculate it?

CPM is the cost per 1,000 ad impressions. Divide your total cost by the number of impressions and multiply by 1,000. Spending $500 on 250,000 impressions is a $2.00 CPM. The M is the Roman thousand, from mille, which is why CPM is not cost per million.

Is a $20 CPM high?

It depends entirely on what you are buying. Broad display inventory often runs $1 to $5, social sits in the mid single digits, and tightly targeted business audiences, connected TV and podcasts can run $20 to $50 and be perfectly reasonable. A CPM is only comparable between two placements when the audience, the format and the viewability are alike.

What is the difference between CPM and RPM?

They are the same transaction seen from the two ends. CPM is what the advertiser pays per 1,000 impressions. RPM is what the publisher receives per 1,000 pageviews. They are never equal, partly because the platform takes a share, and partly because one pageview can carry several ad impressions, so the two are not even counting the same thing.

Does CPM tell me how many people saw my ad?

No, and this is the most common misreading of it. Impressions count how many times an ad was served, not how many people saw it. Impressions divided by reach gives frequency, and a million impressions can be a million people once or a hundred thousand people ten times. Both quote the same CPM.

What counts as a viewable impression?

The Media Rating Council standard is at least 50 percent of the ad's pixels in view for at least one continuous second, and two seconds for video. Impressions that never met that bar were still billed, so if your campaign ran at 60 percent viewability your effective cost on the impressions that had a chance of working is about 1.67 times the CPM you were quoted.

How do I convert CPM to CPC?

Divide the CPM by 1,000 to get the cost of one impression, then divide by your click rate. A $10 CPM at a 0.5 percent click rate is a $2.00 cost per click. Every CPM buy has a cost per click hiding inside it, and the click rate is the only thing that sets it.

Why do my three numbers not agree?

If you enter cost, impressions and CPM and they do not reconcile, this page recalculates the CPM from your cost and impressions and tells you so. Cost and impressions are things that were measured. The CPM is what falls out of them, so when they disagree the CPM is the one that should move.

Is a lower CPM always better?

No. A CPM is a price, not a result. Cheap impressions in front of the wrong people are the most expensive thing you can buy, and the cheapest inventory is usually cheap for a reason, whether that is poor viewability, a low quality placement or an audience that will never care. Judge a campaign on cost per customer, not cost per thousand.

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