Skip to main content

Understanding eCPM

eCPM — Effective Cost Per Mille — tells you how much revenue your inventory generates per 1,000 ad impressions. It is the best single indicator of monetisation efficiency, and the metric most worth watching over time. A rising eCPM means buyers are valuing your inventory more. A falling eCPM means demand is softening — and understanding why is the key to reversing it.

How eCPM is calculated​

eCPM = (Total Earnings ÷ Total Impressions) × 1,000

Example

You earned €180 from 400,000 impressions this week. eCPM = (180 ÷ 400,000) × 1,000 = €0.45. Next week, earnings rise to €220 from the same 400,000 impressions. eCPM = €0.55. The inventory is the same — buyers are simply paying more for it.

The main factors that drive eCPM​

eCPM is not a fixed property of your site — it moves in response to demand conditions, audience signals, and inventory quality. The factors that have the most direct impact:

  • Consent rate — when users accept personalised advertising, buyers can use audience data to target them. This increases the value and competitiveness of your inventory in the ad auction.
  • Viewability — inventory that is demonstrably seen by real users commands higher CPMs. Buyers pay more for ads they know are visible, and many campaigns enforce minimum viewability thresholds.
  • Seasonality — Q4 (October–December) consistently delivers the highest eCPMs of the year as advertisers exhaust annual budgets. January is typically the weakest month. A January eCPM dip is expected, not alarming.
  • Demand mix — private marketplace deals and direct demand generally yield higher eCPMs than open auction. The composition of your demand sources matters.
  • Fill rate and competition — more buyers competing for the same impression pushes prices up. Header bidding is designed to maximise this competition.

Why eCPM is an average — and why that matters​

The eCPM shown on the Performance page is an average across all your impressions in the selected period. It can mask significant variation underneath. A domain with an eCPM of €2.00 and 50,000 monthly impressions contributes €100. A domain with an eCPM of €0.40 and 1,000,000 monthly impressions contributes €400. The second domain earns more despite a far lower eCPM.

Use the Reports page to break eCPM down by domain, product, or device to see where the variation is. This is where the diagnostic value lies.

Practical tips
  • If your eCPM drops suddenly and your impression volume is unchanged, the first two things to check are your consent rate and your ads.txt status. Both can cause an eCPM drop overnight.
  • Comparing eCPM across devices in the Reports page almost always reveals a desktop-mobile gap — desktop eCPM is typically higher. Quantifying this gap helps you understand how a shift in device mix affects overall revenue.

See also: What counts as an impression? · Understanding consent rate · What is viewability and why does it matter? · RPM vs eCPM: what is the difference?