In brief: CPM is the cost per thousand ad impressions. It enables reach-buying comparisons, but alone says nothing about attention, audience quality, or business results.
How I use CPM (Cost Per Mille) in practice
I care about trend and cause, not an isolated CPM value. I break results down by source, offer, or customer type, but only as far as enough data remains for a sensible decision. Every dashboard should note alongside the number what changed in measurement or operations.
What to watch out for
The number looks more precise than it is. CPM can be distorted by poor implementation, consent, attribution rules, small data volumes, or different tool definitions. Optimizing a metric without checking business results often means producing cheaper but worse activity.
Questions for decisions
- How exactly is the value calculated and from which source?
- Which decision changes when the number rises or falls?
- What could distort or duplicate measurement?
- What do we compare the value with so it has business meaning?