RPM, eCPM & viewability calculator

Questions

What is the difference between RPM and eCPM?

RPM is revenue per thousand pageviews; eCPM is revenue per thousand ad impressions. They differ by how many ad slots each pageview fills and how many of those actually render. A page with four viewable slots produces roughly four impressions per pageview, so its RPM can be several times its eCPM. Comparing one site’s RPM to another site’s eCPM is the single most common way ad ops numbers get misread.

How do you calculate RPM?

RPM = (total revenue ÷ total pageviews) × 1000. So $250 from 100,000 pageviews is a $2.50 RPM. Session RPM uses sessions instead of pageviews and is the better number when you want to know what a visitor is worth rather than what a page is worth.

How do you calculate eCPM?

eCPM = (total revenue ÷ total impressions) × 1000. It normalises earnings across deals bought on different models — CPC, CPA and fixed-price sponsorships all reduce to a comparable per-thousand-impression figure.

What counts as a viewable impression?

Under the MRC standard, a display ad is viewable when at least 50% of its pixels are in the viewport for at least one continuous second. Large display units of 242,500 pixels or more need 30% for one second. Video needs 50% of pixels for two continuous seconds. Viewability rate is viewable impressions ÷ measured impressions, and measured is always lower than served because some impressions cannot be measured at all.

Why is my viewable CPM higher than my eCPM?

Because vCPM divides the same revenue across only the viewable subset of impressions. If half your impressions are viewable, your vCPM is roughly double your eCPM. Buyers purchasing on a vCPM basis pay only for viewable impressions, so raising viewability raises what your inventory earns without needing more traffic.