Advertising metrics describe different stages of an impression's journey. The names sound similar, but CPM, fill rate and eCPM answer different questions. Knowing the denominator is essential when comparing monetisation proposals.
CPM is a price per thousand
CPM means cost per thousand ad impressions. When a campaign pays a $2.50 CPM for 800,000 filled impressions, the gross amount is 800,000 ÷ 1,000 × $2.50, or $2,000. This example is arithmetic, not a quote from any advertising partner.
Fill rate changes the outcome
Imagine 1,000,000 available ad impressions and an 80% fill rate. That produces 800,000 filled impressions. At $2.50 CPM, gross revenue would be $2,000. If a publisher receives 85% of gross revenue, publisher revenue would be $1,700.
Define the effective denominator
Net eCPM across all available impressions in that example is $1,700 ÷ 1,000,000 × 1,000 = $1.70. If a network reports eCPM against only filled impressions, it will show a different figure. Always ask how impressions are counted.
Compare partnerships on more than CPM
Ask about reporting transparency, viewability, ad formats, geography, fill rates, brand safety, support, revenue share, payout threshold, Net 30 settlement, invoicing, and technical compatibility. Responsive ad formats and a good reader experience matter as much as a headline CPM.
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