eCPM (effective cost per mille)
Revenue or cost per thousand impressions, calculated after the fact for any pricing model, so that campaigns or placements bought by click, by action or by impression can be compared on one scale. Publishers use it to see which placements earn most; advertisers use it to compare what they really paid. It compares the price of impressions, not their quality, so a cheap eCPM on unseen or invalid impressions is not a bargain.
Where it's used
Used by publishers and ad networks to rank placements and by media buyers to compare CPC, CPA and CPM deals. Good as a common currency, read together with viewability and outcomes.
How to calculate it
eCPM = Revenue ÷ Impressions × 1,000
Worked example
Illustrative numbersA publisher earns 1,200 from a CPC deal that served 400,000 impressions and 900 from a CPM deal that served 200,000 impressions.
eCPM of the CPC deal
1,200 revenue ÷ 400,000 impressions × 1,000 = 3.00
eCPM of the CPM deal
900 revenue ÷ 200,000 impressions × 1,000 = 4.50
What it tells you
The CPC deal brings in more money in total, but each thousand impressions earns half as much again on the CPM deal. Give the CPM buyer the scarce placements.