Metric wiki
What is eCPM?
By Oliver Wakefield-Smith · updated July 2026
The short answer
eCPM, effective cost per mille, is total earnings divided by total impressions, times 1,000. It converts any mix of pricing models into one per-thousand number. Plain CPM is a price you agreed; eCPM is a result you measured. Publishers and ad networks live in eCPM because it makes unlike inventory comparable.
eCPM = total earnings ÷ total impressions × 1,000
Mixed revenue: $300 from CPC clicks + $120 from CPM deals + $60 from a CPA payout = $480
$480 ÷ 200,000 impressions × 1,000 = $2.40 eCPM
AdMob and other network dashboards report exactly this computation over your traffic.
Who uses it and why
A publisher running three demand sources cannot compare a CPC deal to a CPM deal by their contract terms; converted to eCPM over the same impressions, the better payer is arithmetic. Ad networks report eCPM for the same reason: it is the universal exchange rate of monetization. Advertiser-side platforms run the mirror-image conversion internally when they rank CPC bids in an impression auction, which is worked at CPM vs CPC.
Why your network's eCPM differs from your contracted CPM
- Unfilled impressions. eCPM divides by ALL impressions; unfilled ones add zeros to the denominator.
- Mixed pricing underneath. A blended report can sit above or below any single contract in it.
- Count discrepancies. Your server and the network count impressions differently; the divergence taxonomy is at CPM vs eCPM.
Related: RPMis the same computation with a platform's revenue-share already subtracted; the AdSense page shows both live, and the formula page holds the base arithmetic.