Stands for "Revenue Per Mille." The word "mille" means "one thousand" in Latin, so RPM is short for "Revenue Per 1,000 Impressions" in online advertising. It is similar to CPM, but measures the revenue from 1,000 ad impressions instead of the cost of the ads. Advertisers typically focus on CPM, while publishers monitor RPM.
RPM is calculated from ad impressions and overall revenue. For example, a website that gets 20,000 page views per day and generates $300 in daily ad revenue has a page RPM of $15.00.
$300 revenue / 20,000 page views x 1,000 = $15.00 RPM
If a website gets 10,000 page views each day and the page RPM is $5.00, the website will produce $50/day of advertising revenue.
10,000 page views x ($5.00 / 1,000 RPM) = $50 revenue
Page RPM vs Impression RPM
Two specific types of RPM are "Page RPM" and "Impression RPM." The above examples use page RPM since they are based on page views. Impression RPM, or ad unit RPM, measures the revenue per 1,000 impressions of a specific ad unit. If a webpage only has one banner ad, the page RPM and impression RPM will be identical. If a page has more than one ad unit (which is often the case), the individual ads will typically have lower impression RPMs than the page RPM. If certain ads have low RPMs, a publisher may replace or remove them with the goal of generating higher page RPMs.
Page RPM vs eCPM
In some cases, RPM and CPM are used interchangeably. While CPM means "Cost Per 1,000 Impressions," some advertising platforms use CPM in publisher reports instead of RPM. Specifically, the metric "eCPM" or "effective CPM" is sometimes used in place of "page RPM." While "page RPM" is more accurate, "eCPM" in a publisher advertising report means the same thing.
Revolutions Per Minute
Outside of advertising, RPM typically stands for "Revolutions Per Minute." In hardware specifications, RPM may refer to fan speed or hard drive rotational speed. Faster HDD speeds provide lower seek times, which translate to faster data access. The standard rotational speed of a 3.5" hard drive in a desktop computer is 7,200 RPM, while portable hard drives often run at 5,400 RPM. High-end server HDDs run at 10,000 or even 15,000 RPM.