How to Calculate CPM: A Simple Step-by-Step Guide
CPM stands for Cost Per Mille, which means the cost of showing an advertisement 1,000 times.
It is commonly used in display advertising, social media campaigns and brand-awareness campaigns where advertisers want to understand how much they are paying for ad exposure.
In this guide, you’ll learn how to calculate CPM, understand the formula, interpret the result, and compare advertising costs across different campaigns.
By ToolNestPro | Updated September 2026
What Is CPM?
CPM stands for Cost Per Mille, with “mille” meaning one thousand.
It shows how much you are paying for every 1,000 ad impressions.
For example, if you spend £200 and your advert receives 50,000 impressions:
CPM = (£200 ÷ 50,000) × 1,000
CPM = £4
This means you paid £4 for every 1,000 impressions.
CPM is useful when comparing the cost of reaching audiences across different campaigns or advertising platforms.
The basic CPM formula is:
CPM = (Total Advertising Cost ÷ Total Impressions) × 1,000
For example, if you spend £300 on a campaign and receive 75,000 impressions:
CPM = (£300 ÷ 75,000) × 1,000
CPM = £4
This means you are paying £4 for every 1,000 impressions.
CPM is especially useful for comparing campaigns focused on reach and visibility rather than clicks or conversions.
How to Calculate CPM
Your CPM tells you how much you are paying to show your advert 1,000 times.
A lower CPM means you are reaching more people for the same budget, while a higher CPM means your ad exposure is costing more.
However, a low CPM is not automatically better.
For example:
Campaign A has a CPM of £3
Campaign B has a CPM of £8
Campaign A is cheaper for reach, but Campaign B may still be more valuable if it reaches a more relevant audience or leads to stronger results.
That is why CPM should be considered alongside other metrics such as CTR, CPC, conversions and ROAS.
CPM is easy to calculate, but the result can be misleading if the wrong figures are used.
Common mistakes include:
using clicks instead of impressions
forgetting to multiply by 1,000
using only part of the campaign cost
comparing campaigns with very different audiences or objectives
assuming a lower CPM always means better performance
ignoring whether the impressions are reaching the right people
For example, a campaign with a very low CPM may still perform poorly if the advert is being shown to people who are unlikely to become customers.
That is why CPM should be used together with other advertising metrics rather than judged on its own.
How to Interpret Your CPM
Common CPM Calculation Mistakes
Calculate Your CPM
Frequently Asked Questions
What does CPM mean in advertising?
CPM stands for Cost Per Mille and shows how much you pay for every 1,000 ad impressions.
What is a good CPM?
There is no single good CPM because it depends on the platform, audience, industry and campaign objective.
Is a lower CPM always better?
Not necessarily. A lower CPM means cheaper reach, but the audience still needs to be relevant and useful to your campaign.
Want to quickly work out how much you are paying for every 1,000 ad impressions?
Use our free CPM Calculator to enter your total ad spend and impressions and calculate your cost per thousand impressions instantly.