Why is my eCPM lower than my CPM floor?

Because the floor only governs impressions that actually filled, while eCPM is calculated across all the impressions in the report. Any unfilled, passback or house-ad volume dilutes the average. A $2.00 floor with 60% fill and nothing earned on the remainder produces an eCPM of about $1.20.

Should eCPM be calculated on gross or net revenue?

State which one you mean, because both are used. Publishers usually quote eCPM net of the platform's share, since that is what they are paid. Sell-side platforms often report gross. A 15% fee difference is enough to make two correct eCPM figures look like a discrepancy.

Does eCPM include ad requests that never returned an ad?

Only if your impression count does. eCPM is a straight division, so it inherits whatever the denominator includes. If you want fill effects visible in the number, divide by requests; if you want the rate on delivered inventory, divide by impressions. Say which you did.

eCPM Calculator

Work out effective CPM from what a placement actually earned and how many impressions it actually served. Unlike a contracted CPM, eCPM is a result rather than a rate you agreed — which is why it rarely matches the number on the insertion order.

Total earnings

Impressions

eCPM

$—

Enter both figures to calculate.

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Formula

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

Divide earnings by impressions to get revenue per impression, then multiply by 1,000. The multiplier is the whole point of the metric — dropping it is the most common spreadsheet error in ad ops reporting.

eCPM and CPM are not the same number

A CPM is a price you negotiated. An eCPM is what fell out the other end after everything that happened to the inventory in between — unfilled requests, passbacks, discrepancies, fee deductions. That is why a publisher running a $2.00 floor reports a blended eCPM well below $2.00: the floor applies to filled impressions, while the eCPM is spread across everything that was counted. If your eCPM matches your CPM exactly, that usually means you are looking at a single fully-delivered line item rather than a blend.

Check which denominator you are comparing

The most common way eCPM comparisons go wrong is mismatched denominators. A DSP counts impressions it bought and won; an ad server counts impressions it served; a verification vendor counts impressions it measured. Those three numbers differ by a few percent on a good day and far more when discrepancies creep in. Before concluding that a placement underperformed, confirm both eCPMs were calculated over the same impression count from the same system.

Frequently asked questions

Why is my eCPM lower than my CPM floor?: Because the floor only governs impressions that actually filled, while eCPM is calculated across all the impressions in the report. Any unfilled, passback or house-ad volume dilutes the average. A $2.00 floor with 60% fill and nothing earned on the remainder produces an eCPM of about $1.20.
Should eCPM be calculated on gross or net revenue?: State which one you mean, because both are used. Publishers usually quote eCPM net of the platform's share, since that is what they are paid. Sell-side platforms often report gross. A 15% fee difference is enough to make two correct eCPM figures look like a discrepancy.
Does eCPM include ad requests that never returned an ad?: Only if your impression count does. eCPM is a straight division, so it inherits whatever the denominator includes. If you want fill effects visible in the number, divide by requests; if you want the rate on delivered inventory, divide by impressions. Say which you did.