eCPM

Effective cost per mille (eCPM) is the actual cost per thousand impressions, calculated as total spend divided by impressions, multiplied by 1,000 — regardless of how the campaign was priced. A CPI campaign still has an eCPM, which shows what the impressions effectively cost.

eCPM is useful for comparing supply sources, formats and markets on a common basis. On the publisher side, eCPM measures revenue per thousand impressions. For advertisers, a rising eCPM with stable conversion rates means costs are increasing; a higher eCPM with a stronger conversion rate can still mean cheaper outcomes. Read eCPM together with IPM and eCPI rather than on its own.

A practical habit is to chart eCPM and conversion rate together by source over time, so that price changes are always read in the context of the results they buy. That prevents cutting inventory that looks expensive but actually delivers cheap outcomes.