CPM formula
CPM = cost ÷ impressions × 1,000
Take the ad cost, divide it by the number of times the ad was shown, then multiply the result by 1,000. The same formula gives you the third after you have two of the three numbers.
How to calculate CPM, cost or impressions
| To find | Formula | Worked example |
|---|---|---|
| CPM | cost ÷ impressions × 1,000 | $500 ÷ 100,000 × 1,000 = $5.00 Open in the calculator |
| Total cost | CPM × impressions ÷ 1,000 | $8.00 × 1,000,000 ÷ 1,000 = $8,000.00 Open in the calculator |
| Impressions | cost ÷ CPM × 1,000 | $5,000 ÷ $12.50 × 1,000 = 400,000 Open in the calculator |
| Cost per impression | CPM ÷ 1,000 | $5.00 ÷ 1,000 = $0.0050 Open in the calculator |
Because the impressions formula divides by the CPM, a price rise hurts a bit less than it first appears. If the CPM rises 10% from $12.50 to $13.75, $5,000 purchases 363,636 impressions, compared with 400,000 before, a drop of 9.1% rather than 10%.
What gets counted as an impression
An impression means one time an ad appears on a screen. Under the IAB ad impression guidelines, an impression is counted as late as possible during delivery. This happens once the ad reaches the viewer's browser, and bot traffic is filtered out. A counted impression doesn't prove that someone looked at the ad.
CPM formula in Excel and Google Sheets
Enter CPM in C2, impressions in B2 and cost in A2. Both programs use these formulas in the same way.
| To find | Cell formula |
|---|---|
| CPM | =ROUND(A2/B2*1000, 2) |
| Total cost | =ROUND(C2*B2/1000, 2) |
| Impressions | =ROUND(A2/C2*1000, 0) |
| Cost per impression | =ROUND(C2/1000, 4) |
ROUND trims each answer to the number of decimals this calculator shows. If you want to keep every decimal, leave it out.
How the calculator handles rounding
- Money is shown with 2 decimals, for example $5.00.
- When money is under one cent, the display uses 4 decimals, such as $0.0050.
- When money is under a hundredth of a cent, the display uses 6 decimals, such as $0.000050.
- For impressions, whole numbers are used. A half rounds up. At a $12 CPM, $1,000 gives 83,333.33 impressions. The calculator displays 83,333, while a spreadsheet without ROUND displays 83,333.33.
Check cost per impression for the price of one view at common CPMs.