Cost Per Mille (CPM)
Cost per mille is the advertising cost per thousand impressions; “mille” means one thousand.
What is Cost Per Mille?
CPM measures the price of exposure rather than the price of a click or sale. An impression is a counted display of an ad under the platform’s measurement rules. It is not necessarily a unique person seeing the campaign.
A report can express effective CPM even when the campaign was bought under another charging model. The calculation normalizes spend against impressions; it does not by itself explain how the platform billed each interaction.
CPM = Ad spend ÷ Impressions × 1,000
Use impressions and spend from the same scope. Standard served impressions and viewable impressions are different denominators; a viewable CPM should be labeled accordingly.
Buying 150,000 impressions
A home-fragrance campaign spends $900 and receives 150,000 impressions. Its CPM is $6. If those impressions reach 50,000 people, average frequency is three impressions per person. The campaign did not reach 150,000 different shoppers.
How to interpret it
CPM describes the cost of reaching an advertising opportunity. A lower CPM means more counted impressions per dollar, but those impressions may occur in different contexts or among people with different purchase intent.
Compare like placements and objectives. Premium audiences, video inventory and narrow remarketing lists can have different costs. A change in campaign mix can move the overall CPM even when the price within each placement has barely changed.
Repeated exposure matters. Rising frequency can consume impressions without adding many new people. CPM and reach together help distinguish the price of displaying ads from the breadth of the audience reached.
To connect CPM with click economics, keep CTR on the same impression and click basis. At a 1% CTR, 1,000 impressions produce ten clicks; a $6 CPM would imply an average $0.60 per click under those matched figures. That relationship still says nothing directly about profit.
Common mistakes
Treating impressions as unique reach
One person can generate several impressions. Reach counts people or accounts under a platform rule; impressions count exposures.
Comparing served and viewable CPM without qualification
A lower cost per served impression can conceal limited viewability. Measurement standards are part of the metric definition.