To calculate the CPM, divide your total ad cost by your total impressions, then multiply by 1,000. That is the whole formula. This guide walks through it step by step, then shows worked examples, spreadsheet formulas, common mistakes and a few practice questions you can try yourself.
New to the term? Read What Is CPM? first for the meaning and background. This page focuses only on the calculation.
The CPM Formula
Dividing cost by impressions gives you the price of a single impression, which is usually a tiny fraction of a cent. Multiplying by 1,000 turns that into a number that is easier to read and compare: the price of 1,000 impressions.
3 Steps to Calculate the CPM
Step 1: Find your total cost
Use the full amount spent on the campaign, in a single currency. Include only the spend for the period you are measuring.
Step 2: Find your total impressions
Take the impressions figure from your ad dashboard for the same campaign and the same dates. Impressions count every time the ad was shown, so do not use reach, clicks or views here.
Step 3: Divide, then multiply by 1,000
Divide cost by impressions, then multiply the result by 1,000. Round only at the end, so small amounts do not get lost along the way.
Worked Examples
Here are four campaigns with the working shown, so you can follow every step.
| Cost | Impressions | Working | CPM |
|---|---|---|---|
| $500 | 200,000 | (500 ÷ 200,000) × 1,000 | $2.50 |
| $1,200 | 450,000 | (1,200 ÷ 450,000) × 1,000 | $2.67 |
| $80 | 25,000 | (80 ÷ 25,000) × 1,000 | $3.20 |
| $3,000 | 1,200,000 | (3,000 ÷ 1,200,000) × 1,000 | $2.50 |
Notice that the first and last campaigns have the same CPM even though one spent six times more. CPM measures the price of reach, not the size of the budget.
Work Backwards: Cost and Impressions
The same formula can be rearranged. If you know any two values, you can find the third.
| Find the cost | Cost = (CPM × Impressions) ÷ 1,000 |
| Find the impressions | Impressions = (Cost ÷ CPM) × 1,000 |
Cost example: a $8 CPM across 250,000 impressions costs (8 × 250,000) ÷ 1,000 = $2,000.
Impressions example: a $1,500 budget at a $6 CPM buys (1,500 ÷ 6) × 1,000 = 250,000 impressions.
Examples by Platform
The method is identical on every platform. Only the numbers change. These are illustrative figures to practise with, not benchmarks.
| Platform | Cost | Impressions | CPM |
|---|---|---|---|
| Google Display | $200 | 100,000 | $2.00 |
| Facebook Ads | $350 | 40,000 | $8.75 |
| TikTok Ads | $420 | 50,000 | $8.40 |
| YouTube Ads | $900 | 60,000 | $15.00 |
Want a platform-specific tool? Try our YouTube CPM calculator, Facebook Ads CPM calculator or TikTok CPM calculator.
Calculate CPM in Excel or Google Sheets
Put the cost in column B and impressions in column C. In cell D2, enter:
To avoid an error when a row has zero impressions, wrap it like this:
Drag the formula down the column and you have a CPM for every campaign. To get the CPM for the whole sheet, divide the sum of the cost column by the sum of the impressions column, then multiply by 1,000. Do not average the individual CPMs, because campaigns with more impressions should count for more.
Common Mistakes When You Calculate CPM
- Using clicks instead of impressions. CPM needs impressions. Clicks give you CPC, a different metric. See our CPC calculator.
- Using reach instead of impressions. Reach counts people, impressions count every showing. One person can see your ad several times.
- Mixing time periods. Spend from the whole month with impressions from one week gives a wrong CPM.
- Mixing currencies. Convert everything to one currency before you divide.
- Averaging CPMs. Add up total cost and total impressions first, then calculate once.
- Publishing numbers without checking. If you are a publisher measuring earnings rather than spend, you want eCPM instead. Use the eCPM calculator.
Practice Questions
Try each one yourself, then open the answer to check.
1. You spent $240 and got 80,000 impressions. What is the CPM?
(240 ÷ 80,000) × 1,000 = $3.00.
2. Your CPM is $4.50 and you want 300,000 impressions. What will it cost?
(4.50 × 300,000) ÷ 1,000 = $1,350.
3. You have a $600 budget and a $5 CPM. How many impressions can you buy?
(600 ÷ 5) × 1,000 = 120,000 impressions.
🎯 Key Takeaways
- CPM = (Total Cost ÷ Total Impressions) × 1,000
- Use cost and impressions from the same campaign and the same dates
- Rearrange the formula to find total cost or impressions from your budget
- In a spreadsheet, use =(B2/C2)*1000 and add IFERROR for empty rows
- Do not confuse impressions with clicks or reach
Frequently Asked Questions
How do you calculate the CPM?
Divide your total ad cost by your total impressions, then multiply by 1,000. For example, $500 spent on 200,000 impressions gives a CPM of $2.50.
Why do you multiply by 1,000 when you calculate CPM?
CPM means cost per mille, and mille is Latin for one thousand. Dividing cost by impressions gives the cost of one impression, so multiplying by 1,000 scales it to the cost of 1,000 impressions.
How do I calculate CPM in Excel or Google Sheets?
If cost is in cell B2 and impressions are in C2, use =(B2/C2)*1000. Wrap it in IFERROR to avoid errors when impressions are zero.
Can I calculate CPM from clicks?
Not directly. CPM needs impressions. If you only know your cost per click and click-through rate, you can estimate it with CPM = CPC × CTR × 10, where CTR is a percentage.
How do I work out how many impressions my budget will buy?
Divide your budget by your CPM and multiply by 1,000. A $600 budget at a $5 CPM buys 120,000 impressions.
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