What Is eCPM? A Plain-English Guide for App Developers

The one-sentence definition

eCPM stands for effective cost per mille — the revenue you earn for every 1,000 ad impressions. (“Mille” is Latin for thousand, the same root as “millennium.”) It is the number that lets you put every ad, every deal, and every network on one comparable scale, which is why it shows up on almost every monetization dashboard you will ever open.

If you only remember one thing from this page, make it this: eCPM is an output, not a rate you set. You do not choose your eCPM. It is what falls out after advertisers bid, some impressions go unfilled, and the network takes its cut. Treating it as a dial you control is the most common beginner mistake.

The formula, and a worked example

eCPM = (total ad revenue ÷ total impressions) × 1,000

Say your app showed 240,000 ad impressions last month and your networks paid out $780. Your eCPM is ($780 ÷ 240,000) × 1,000 = $3.25. That single figure now lets you compare this month to last month, this network to that one, or a banner placement to a rewarded one — even though the underlying deals were priced in completely different ways.

The formula runs backwards just as usefully. If you know a placement earns roughly a $12 eCPM and you expect 50,000 impressions next month, your forecast is 50,000 ÷ 1,000 × $12 = $600. That is exactly the calculation the revenue calculator runs for every ad format you enable, then adds together.

Why the “effective” matters

The “e” is doing real work. A single thousand impressions is almost never sold as one clean block. Some are filled by a fixed-price CPM buy, some by a cost-per-click campaign that only pays when a user taps, some by a cost-per-install deal, and a few by house ads that earn nothing at all. eCPM blends all of that into one per-thousand figure so you never have to untangle how each individual impression was sold. It also quietly bakes in your fill rate — the share of ad requests that actually returned a paid ad. A high nominal CPM with 40% fill can lose to a lower CPM with 95% fill, and eCPM is where that shows up.

eCPM vs CPM vs RPM vs CPC/CPI

These acronyms get used interchangeably in forums, and that sloppiness causes real confusion. Here is how they actually differ:

The distinction that trips people up most is eCPM vs RPM. On mobile you count impressions and one screen can show several ads, so eCPM is the norm. On the web you count pageviews and a single page might hold three or four ad slots, so networks report RPM instead. Same idea, different denominator — never compare the two numbers directly.

The four things that move your eCPM

eCPM is not one number; it is a different number for every combination of format, place, and person. Four factors explain the vast majority of the swing, and they compound:

1. Ad format

This is the biggest single lever. A rewarded video can earn ten times or more what a banner in the same app earns, because the user chose to watch it and advertisers pay up for that attention. In round Tier-1 numbers, rewarded video sits in the mid-$20s while a banner scrapes along near a dollar. If you want the format-by-format breakdown, the rewarded vs interstitial guide covers it.

2. Geography

Advertisers pay far more to reach a user in the United States, the UK, Canada, or Australia than one in many parts of Asia, Latin America, or Africa — often five to ten times more for the exact same ad. This is why the calculator’s geographic-mix slider has such an outsized effect: it is blending across three demand tiers, and a US-heavy audience simply prints more money per impression than an emerging-market one.

3. Platform and category

iOS users are treated as higher value and typically earn around 30% more than comparable Android users, so the calculator applies a 1.3× premium to iOS. Category matters too: a finance app pulls high-CPC advertisers and can more than double a casual game’s eCPM, while a hypercasual title with a huge but low-intent audience earns less per impression and has to make it up on volume.

4. Season

eCPMs are not flat across the year. They climb through Q4 as advertisers spend holiday budgets, peak in December, then fall off a cliff in early January when those budgets reset. A December eCPM can run 40–50% above the February low for the same inventory. If you benchmark your app against a December screenshot in March, you will think something broke when nothing did.

A full worked example

Put the pieces together. Imagine a casual game with 10,000 daily active users, a roughly balanced global audience, running one format: three rewarded videos per user per day at a blended $9 eCPM.

• Daily impressions: 10,000 × 3 = 30,000
• Daily revenue: 30,000 ÷ 1,000 × $9 = $270
• Monthly revenue: $270 × 30 ≈ $8,100

Now change one input. Shift that audience from balanced to mostly Tier-1, and the blended rewarded eCPM might climb toward $20 — more than doubling the same app’s revenue without a single extra user. That sensitivity is the whole reason eCPM, not raw downloads, is the number to watch.

Common mistakes to avoid

• Comparing eCPM to RPM. Different denominators. A $6 mobile eCPM and a $6 web RPM are not the same performance.
• Chasing a headline eCPM with terrible fill. A network quoting a $30 eCPM that fills 30% of your requests earns you less than a $12 eCPM at 95% fill.
• Reading one day as a trend. eCPM is noisy day to day. Judge it over weeks, and always against the same season.
• Ignoring the blend. A rising overall eCPM can hide a collapsing banner rate if rewarded volume is growing. Track it per format.

How to actually use it

Track eCPM by format, by geography, and by network, and the story of where your money comes from writes itself — usually a small number of placements and regions carry the whole thing. New to the formats? Read the rewarded video vs interstitial breakdown next, or skip straight to putting your own numbers in.

Calculate your estimated earnings →