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Marketing glossary
What is cost per mille (CPM)?
CPM turns the cost of exposure into a comparable rate. It is most useful when your objective is to make a relevant audience notice or remember you, but it cannot tell you whether that attention produced a worthwhile business result.
What cost per mille means
“Mille” is Latin for one thousand. An advertising platform counts impressions and reports what you paid for each block of 1,000. One person may generate several impressions, so CPM does not normally mean the cost of reaching 1,000 different people.
The formula is:
CPM = advertising cost ÷ impressions × 1,000
If a campaign costs £600 and delivers 100,000 impressions, its CPM is £6. A second campaign costing £300 for 30,000 impressions has a £10 CPM. The first bought exposure more cheaply, although that does not automatically make it the better campaign.
A practical SME example
Imagine that a Birmingham accountancy firm wants local company directors to recognise its name before a seminar. It runs LinkedIn ads to a narrow professional audience and pays £900 for 60,000 impressions. Its CPM is £15.
The firm should then look beyond that number. Did the intended job roles see the adverts? Did frequency become excessive? Did branded searches, seminar registrations or direct enquiries rise? A low CPM obtained by showing adverts to irrelevant people is cheap waste, which remains waste despite the attractive spreadsheet cell.
Why CPM matters
CPM is useful for:
- comparing the price of exposure between suitable audiences or platforms;
- planning an awareness campaign from an expected number of impressions;
- spotting changes in auction pressure, audience scarcity or creative performance;
- assessing channels where a click is not the only valuable response.
It also helps explain other pricing models. You can derive an effective CPM after paying per click, per view or per outcome, allowing a like-for-like comparison of media cost. That comparison still needs context: placements, audience quality, viewability and frequency can differ sharply.
Common mistakes
The most common mistake is treating impressions as attention. An advert can technically load without being noticed, understood or remembered. Viewable-impression reporting improves the measure, but it still does not prove that somebody absorbed the message.
Businesses also compare CPMs across unlike audiences. Reaching 1,000 carefully selected operations directors may reasonably cost more than reaching 1,000 broad consumer profiles. Finally, they optimise exclusively for the lowest CPM and allow the platform to chase cheap inventory, even when it sits outside the people they actually need.
Use CPM with reach, frequency, audience fit and a downstream measure such as click-through rate, qualified enquiries or brand-search growth.
Related guides
Related terms
Is a lower CPM always better?
No. A lower CPM means cheaper impressions, not better attention or more valuable customers. Compare audience quality, placements, frequency and business outcomes before deciding which campaign performed better.
What is the difference between CPM and reach?
Reach estimates how many distinct people saw an advert, while impressions count total displays. CPM prices impressions, so repeated exposure to the same person contributes more impressions without increasing reach by the same amount.
Who wrote this
Steve Ward.
Steve founded Epitomise in 2017 after UK, international and global marketing leadership roles, most recently as Global CMO of the Vitec Group’s Videocom Division. He works with SME and technology businesses on strategy, positioning and the execution that follows — more about Steve.
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