How to use it
Tap the figure you want to find in the equation at the top of the calculator: CPM, cost or impressions. The two boxes you need then appear. Type numbers the way they appear in your ads dashboard; commas between thousands are fine, and you can shorten big counts to 250k or 1.5m.
The currency menu only changes the symbol shown next to money figures. It does not convert between currencies, so enter every amount in the same currency.
The formula
The M in CPM is the Roman numeral for 1,000, so CPM means "cost per mille". Google Ads defines it as paying per one thousand views of an ad. Three versions of the same relationship cover every direction:
CPM = cost ÷ impressions × 1,000
Cost = CPM × impressions ÷ 1,000
Impressions = cost ÷ CPM × 1,000
Worked examples
Finding CPM. A display campaign spent $2,400 and served 800,000 impressions. $2,400 ÷ 800,000 = $0.003 per impression, and $0.003 × 1,000 = $3.00 CPM.
Finding impressions from a budget. A publisher quotes $4.20 CPM and you have $500. $500 ÷ $4.20 × 1,000 = 119,047.6, so the budget buys about 119,048 impressions. Impressions come in whole numbers, so the calculator rounds and shows you the exact figure underneath.
Finding the cost of a placement. A newsletter sponsor offers 250,000 impressions at $6.50 CPM. $6.50 × 250,000 ÷ 1,000 = $1,625.00. Each impression costs $0.0065.
| Cost | Impressions | CPM |
|---|---|---|
| $2,400 | 800,000 | $3.00 |
| $500 | 119,048 | $4.20 |
| $1,625 | 250,000 | $6.50 |
CPM, cost per impression and eCPM
Cost per impression is CPM divided by 1,000. It is usually a fraction of a cent, which is why buyers quote the thousand-impression price instead. The calculator shows both.
eCPM, or effective CPM, uses the same formula for campaigns bought some other way. If you paid per click, divide what you spent by the impressions you received and multiply by 1,000, and you can compare that campaign with one bought on CPM. Publishers use the same sum with revenue in place of cost to see what they earned per 1,000 impressions.
Mistakes that skew a CPM
- Mixing periods. Cost from the whole month with impressions from one week gives a CPM four times too high. Take both from the same date range.
- Forgetting the 1,000. Cost ÷ impressions on its own is the cost of one impression. If your answer looks 1,000 times too small, the multiplication is missing.
- Viewable versus served. Google Ads offers viewable CPM (vCPM) bidding, where you pay only when the ad could be seen. A vCPM and a CPM based on every served impression count different things, so compare like with like.
- Fees. If an agency or platform fee sits on top of media cost, decide whether your "cost" includes it, and do the same for every campaign you compare.
How this calculator handles your numbers
Every figure you type is turned into an exact fraction before any division, so the result does not pick up floating-point noise. Money is rounded to two decimals at the end, half away from zero, and a cost that would show as $0.00 is given to four decimals instead. Impression counts are rounded to the nearest whole number. Zero impressions or a zero CPM, where a division would be meaningless, get a plain message instead of an answer.