Market
RPM, CPM, eCPM: getting everyone on the same ruler
CPM is the price per thousand impressions; eCPM is effective revenue per thousand served impressions; RPM is revenue per thousand pageviews. They look like cousins but measure different things — and mixing them is the classic source of proposals that sound great and earn little.
For a publisher, the ruler that matters is page RPM: how much comes in per thousand pageviews, across all formats. It's the only metric that already discounts fill, viewability and everything else standing between the advertised price and the money.
One example of the trick: a high-CPM format with 20% fill can earn less than a modest format that runs on every page. CPM sells well on slides; RPM pays the bills.
That's why every proposal and every report here speaks in RPM over your real pageviews. If someone only gives you CPM, ask for the fill — or just ask for the RPM.
Sources and reading
Google — definição de RPM · IAB