How eCPM is calculated
Divide actual ad revenue by the number of ad impressions and multiply by 1,000. For $750 earned from 50,000 impressions, eCPM is $15. Google AdMob describes eCPM as an estimate of revenue per thousand impressions.
Check what counts as an impression
Ad requests, served responses, rendered impressions, and viewable impressions can produce different denominators. Use one clearly labeled definition and a matching revenue period when comparing results. A higher eCPM can accompany fewer impressions, so review total earnings and fill as well as the rate.