CPM Calculator

How to use the CPM calculator

1. Choose what to solve for. CPM needs the ad spend and the impressions. Cost needs the CPM rate and the impressions you want. Impressions needs a budget and a CPM rate.
2. Enter the two known values from your ad platform’s report or a media kit.
3. Add clicks and conversions if you have them. They are optional and only affect the click-through rate, cost per click and cost per conversion.

The calculator opens on a campaign that spent $500 for 125,000 impressions. Entering 1,000 clicks and 25 conversions fills in the rest of the results.

The CPM formula

CPM stands for cost per mille, Latin for thousand. Google Ads Help describes it as paying per one thousand views, or impressions. The “× 1,000” is there because the cost of a single impression is a fraction of a cent and hard to compare.

• CPM from spend: $500 ÷ 125,000 × 1,000 = $4.00. Each impression cost $0.004.
• Impressions from a budget: $1,200 at an $8.00 CPM buys 1,200 ÷ 8 × 1,000 = 150,000 impressions.
• Cost of a plan: 150,000 impressions at $8.00 cost 8 × 150,000 ÷ 1,000 = $1,200.

CTR, CPC and cost per conversion

Impressions are only the first step. The same campaign data gives three more ratios:

• Click-through rate (CTR) = clicks ÷ impressions. Google Ads Help gives the example of 5 clicks from 100 impressions, a 5% CTR. In the opening example, 1,000 clicks from 125,000 impressions is a 0.8% CTR.
• Cost per click (CPC) = cost ÷ clicks: $500 ÷ 1,000 = $0.50.
• Cost per conversion = cost ÷ conversions: $500 ÷ 25 = $20.00. Its conversion rate is 25 ÷ 1,000 = 2.5% of clicks.

A low CPM with a very low CTR can cost more per sale than a higher CPM on a placement where people click. CPM measures what attention costs; the other ratios show what it produced.

Comparing a CPM buy with a CPC buy

Some placements are sold per thousand impressions and others per click. To compare them, convert the CPC offer into an effective CPM:

At $0.50 per click and a 0.8% CTR, 1,000 impressions bring 8 clicks, costing 8 × $0.50 = $4.00, which matches the CPM above. Now suppose one site offers a $6.00 CPM and another offers $0.75 per click, where you expect a 0.5% CTR. The CPC offer works out to 0.75 × 0.005 × 1,000 = $3.75 per thousand impressions, lower than $6.00, but only if the CTR estimate holds. Turning it around, the highest CPC you can pay and stay at a $6.00 CPM is 6 ÷ (0.005 × 1,000) = $1.20.

Impressions, reach and frequency

Impressions count every time an ad is shown, not the number of people who saw it. If an average viewer sees an ad three times, 150,000 impressions reach about 150,000 ÷ 3 = 50,000 people. Ad platforms report reach and frequency separately when they can measure them.

When planning for reach, work backward: to show an ad to 40,000 people an average of 4 times, you need 160,000 impressions, and at a $5.00 CPM that is 160,000 × 5 ÷ 1,000 = $800. The impressions mode of the calculator does the reverse, from a budget to an impression count.

Viewable CPM

Not every impression is seen. An ad at the bottom of a page may load without anyone scrolling to it. Google Ads offers viewable CPM (vCPM) bidding, which charges only for impressions measured as viewable; its help page defines a display ad as viewable when at least half of it is on screen for one second or longer, and a video ad when it plays for two seconds.

Because fewer impressions count, a vCPM rate runs higher than a CPM rate for the same spend. If 60% of the impressions in the opening example were viewable, the cost per thousand viewable impressions would be $4.00 ÷ 0.60 = $6.67. Compare vCPM only with vCPM, and CPM with CPM.

For publishers: RPM and eCPM

Sites that show ads use the same formula from the other side. Google AdSense reports RPM, revenue per thousand impressions, as estimated earnings ÷ page views (or ad impressions) × 1,000. Its help page gives two examples: $0.15 from 25 page views is a page RPM of $6.00, and $180 from 45,000 ad impressions is an ad RPM of $4.00.

To use this calculator for RPM, enter earnings as the ad spend and page views or impressions as the impressions. Page RPM and ad RPM differ because one page view can show several ads, so say which one you mean when comparing figures.

Working back from a goal to a budget

CPM is most useful in planning, before any money is spent. Start from the result you want and divide back through each rate:

• Goal: 20 conversions.
• At a 2.5% conversion rate, that takes 20 ÷ 0.025 = 800 clicks.
• At a 0.8% click-through rate, 800 clicks take 800 ÷ 0.008 = 100,000 impressions.
• At a $4.00 CPM, 100,000 impressions cost 4 × 100,000 ÷ 1,000 = $400, or $20 per conversion.

Each rate is an estimate, and small changes compound. If the CTR turns out to be 0.4% instead of 0.8%, the same 800 clicks need 200,000 impressions and the budget doubles to $800. Use your own past campaigns for the rates when you have them, and run a small test before committing the full budget.

Common CPM mistakes

• Forgetting the × 1,000. $500 ÷ 125,000 is $0.004, the cost of one impression, not the CPM.
• Different cost figures. One report may include platform or agency fees and another may not. Use the same cost basis when comparing campaigns.
• Different impression counts. An ad server and an ad platform can count the same campaign slightly differently. Compare figures from the same source.
• Comparing across formats. Video, display and social placements are priced differently, so a CPM that is high for one format can be low for another.

Sources & assumptions

How this calculator gets its numbers. Full method: our methodology.

• CPM = cost ÷ impressions × 1,000; cost and impressions are solved from the same equation.
• CTR = clicks ÷ impressions; CPC = cost ÷ clicks; cost per conversion = cost ÷ conversions.
• Impressions are whatever your ad platform counts; viewable CPM counts only viewable impressions, so it runs higher than CPM on the same spend.
• The publisher-side RPM uses the same formula with earnings in place of cost.

Sources

1. Google Ads Help, Cost-per-thousand impressions (CPM): Definition. CPM as paying per one thousand views (impressions), and viewable CPM, which counts only impressions that can be seen.
2. Google Ads Help, Bid on viewable impressions using viewable CPM. Viewable CPM charges only for impressions measured as viewable: at least 50% of a display ad on screen for one second or longer, or a video ad playing for two seconds or longer.
3. Google Ads Help, Clickthrough rate (CTR): Definition. CTR = clicks ÷ impressions, with the example of 5 clicks from 100 impressions = 5%.
4. Google AdSense Help, Revenue per thousand impressions (RPM). RPM = estimated earnings ÷ page views (or impressions) × 1,000, with the examples $0.15 from 25 page views = $6.00 and $180 from 45,000 impressions = $4.00.

Last reviewed November 2, 2026. Compare CPMs only across the same kind of placement and impression count.