What is CPI (cost per install) in mobile advertising?

Short answer. In mobile app advertising, CPI means cost per install: the amount you pay for each app install your ads drive, calculated as campaign spend divided by the number of installs. AppsFlyer calls it "one of the most used metrics by marketers," and it only tells you what an install cost, not what that user is worth.

(CPI also stands for Consumer Price Index in economics. This page is about the advertising metric.)

Definition

AppsFlyer describes CPI two ways. As a pricing model, it is "a predetermined price that the advertiser agrees to pay the publisher every time a user installs their app as a direct result of an ad served by the publisher." As a measured result, the related term is eCPI (effective CPI), "the de-facto price you are paying for installs as they come in (or after the campaign)." AppsFlyer treats the calculation as interchangeable with eCPI, and on this page CPI means the effective figure.

One detail matters for anyone buying on Meta or Google: AppsFlyer notes that self-reporting networks "will charge advertisers based on CPM (cost per mille or 1,000 impressions viewed) while optimizing towards eCPI." You often pay for impressions and judge the result per install.

Formula

CPI = marketing campaign spend / number of app installs

Because spend can also be written as CPM times impressions, CPI is the same thing as CPM divided by installs per thousand impressions (IPM). That identity is why creative matters so much to CPI: if the same impressions produce more installs, every install costs less.

Worked example (illustration)

These are made-up round numbers. A game spends $10,000 in a week and records 4,000 installs. CPI is $10,000 / 4,000 = $2.50. If a new creative set lifts installs to 5,000 on the same spend, CPI falls to $2.00 without any change to bids or budget.

What a good or bad reading tells you

A falling CPI means you are buying installs more cheaply. It does not mean you are buying better users. AppsFlyer is direct about the limit: installs "aren't a guarantee for in-app engagement," and app owners "must use CPI in conjunction with other engagement metrics such as LTV and ROAS." AppsFlyer also lists what drives the number: "geo, operating system, vertical, ad unit, channel, and of course supply and demand." So a CPI is only comparable to another CPI from the same country, platform and genre.

We do not quote a benchmark CPI here. Published averages vary by source, year, country and genre, and none survives being applied to a different app.

How it is used in app, game and brand advertising

For games and apps, CPI is the headline UA cost and the denominator in payback maths: what you can afford per install depends on LTV. For consumer brands advertising a shopping app the same logic applies; where the goal is a purchase rather than an install, cost per purchase plays the role of CPI.

Common mistakes

1. Optimising CPI in isolation and buying cheap installs that never pay back.
2. Comparing CPI across countries, platforms or genres as if they were one market.
3. Mixing the network's reported CPI with the MMP figure. AppsFlyer notes a self-reporting network's eCPI "will often differ from that calculated by the attribution provider."
4. Treating a CPI drop after a bid change as a creative win, or the reverse.

Flixr's view

Our view: CPI is a creative metric as much as a media one, because it is CPM divided by how many installs each thousand impressions produce. We try to win more conversions per thousand impressions rather than cheaper impressions, and we judge the result on the client's own numbers, not the network's. For the practical version on one channel, see how to lower CPI on AppLovin without cutting spend, and for how we run UA, our user acquisition service.