eCPM, or Effective Cost Per Mille (thousand impressions) is the method of calculating monetization performance based on the revenue earned per 1000 impressions. This is used across various platforms and mechanisms that monetize via display ads including desktop, mobile, in-app, etc.
The higher the eCPM, the more revenue publishers are getting from their ads.
Formula for calculating eCPM is:
eCPM = Total Ad Earnings/(Impressions x 1000)
eCPM is calculated just like how CPM is calculated. This number gives you the total cost of the marketing or advertising campaign divided by the number of impressions that are generated, divided by 1000. This gives you the total cost for a thousand impressions. In digital marketing, you get the actual benefit of it while making comparisons of this value with different buying mechanisms like CPC and CPA.