Recently, we’ve heard some questions about the difference between eCPM (effective cost per thousand impressions) and RPM (revenue per thousand impressions), as the older AdSense interface references eCPM and the newer version shows RPM. We’d like to clarify and let you know that the terms are referring to the same thing: both eCPM and RPM represent your estimated earnings for every 1000 impressions. To calculate this figure, divide your estimated earnings by the number of page views, impressions, or queries that you received, then multiply by 1000. For example, if you earned an estimated $0.20 from 50 page views, then your page eCPM or RPM would equal ($0.20 / 50) * 1000 or $4.00.

Formula:
eCPM or RPM = (Estimated earnings / Number of page views) * 1000