eCPM

The formula

The "effective" is the point. A CPM is a price someone agreed in advance. eCPM is the result, worked out afterwards, and it works whichever way the space was sold.

Worked examples

• A CPC deal. 50,000 impressions, a 0.3% click-through rate and $0.80 a click: 150 clicks earn $120, an eCPM of $2.40.
• A flat monthly deal. $300 for a month in which the slot served 80,000 impressions: an eCPM of $3.75.
• A network. $55 from 50,000 impressions: an eCPM of $1.10.

Side by side, the flat deal earned more than three times what the network did per impression. That comparison is impossible until everything is in the same unit.

eCPM, CPM and RPM

AdSense reports RPM, revenue per thousand, in two forms. Page RPM divides earnings by page views, so it rises when you put more ads on a page. Impression RPM divides by ad impressions, which makes it the same calculation as eCPM. When you compare a network with a direct offer, use the per-impression figure for the same slot, or you are comparing a whole page with a single ad.

Mistakes that make eCPM lie

• Mixing countries. A slot's eCPM moves with where its readers are. Compare like with like.
• Counting house ads. Unpaid impressions pull the average down without telling you anything about demand.
• Ignoring empty requests. A high eCPM on a slot that fills half the time can earn less than a lower one that always fills. Multiply by the fill rate to see what each request is worth.

How Pyrobid reports it

Pyrobid's reports show eCPM alongside impressions, clicks and revenue for each slot and each campaign, with a switch between paid traffic and all traffic, so the unpaid views of your fallback never water the figure down.