Cost Per Mille (CPM)
CPM doesn't measure a campaign's effectiveness. It only measures how much it costs to be seen, before even knowing if whoever saw you was the right person.
“Reaching a thousand people cheaply is worth nothing if nine hundred ninety-five of them will never decide to buy from you.”
Otto GTM ObservatoryA good CPM on the wrong audience remains waste
CPM measures the cost to reach a thousand impressions, regardless of who receives them. In B2B, where the relevant audience is a tiny fraction of the total online population, an apparently competitive CPM obtained on a generic audience is worth less than a higher CPM obtained on an audience filtered by role, industry, and decision-making level.
This metric should therefore be treated as an exposure cost indicator, not an exposure value indicator: useful for comparing platforms or placements at equal audience quality, misleading if used to compare campaigns targeting audiences of different quality.
Anti-patterns
Common mistake: choosing an advertising channel or placement only because it offers a lower CPM, without verifying whether the reached audience actually matches the ideal customer profile.
Second mistake: using CPM as a success metric for campaigns with a lead generation goal, when the relevant metric in that case should be cost per lead or per MQL, not exposure cost.
Practical Application
A company compares two display channels: channel A offers a €4.50 CPM on a generic audience, channel B an €18.90 CPM on an audience filtered by C-level role at companies with more than 200 employees. Despite the CPM being over 4x higher, channel B generates a 38% lower cost per MQL thanks to the quality of the reached audience.