Formula
eCPM = ad revenue ÷ ad impressions × 1,000
“Mille” is Latin for thousand. eCPM is “effective” because it converts any pricing model — per click, per install, per view — into one comparable number: revenue per 1,000 impressions.
Example
A puzzle game shows 150,000 interstitial ads in a week and earns $450.
eCPM = $450 ÷ 150,000 × 1,000 = $3.00
The same week, 60,000 rewarded video impressions earn $720: eCPM $12.00. Rewarded videos usually earn much more per impression because users choose to watch them.
What affects eCPM
- Ad format: rewarded video > interstitial > banner, typically.
- Country: advertisers pay most for users in high-spending markets.
- Platform: iOS users often earn higher eCPMs than Android users.
- Season: eCPMs often rise in Q4, when advertisers spend most, and dip in January.
- Fill rate and mediation: more networks competing for each impression raise the price.
eCPM isn’t the goal
A higher eCPM from more aggressive ads can cost you users. Look at ad revenue per daily active user (ARPDAU) and retention together, and read reviews after changing ad placements — “too many ads” is one of the most common complaints in app reviews and a common reason for churn.
For apps with purchases, compare with ARPU and ARPPU, and see how much a user is worth over time with lifetime value.