Formula and what counts
Cost per install, or CPI, is the main efficiency metric for app marketing. The formula is ad spend divided by installs attributed to that spend. If a campaign spends 3,000 dollars and drives 1,200 installs, CPI is 2.50 dollars. In marketing, CPI never means the consumer price index; that is the economics term most searches for the letters are after.
What counts as an install depends on the measurement setup. On iOS, privacy rules limit attribution, so platform-reported installs and your measurement partner's numbers can disagree. Note the source next to the figure whenever you share it.
Why CPI alone misleads
An install is not a customer. A cheap install from someone who opens the app once and leaves is worth less than an expensive one from someone who subscribes. Track cost per trial, cost per subscriber or cost per paying user as well, and use them to judge creative; this is the app version of cost per acquisition.
Different creatives attract different users. A playful trend video may win on CPI while a creator showing the app solving a real problem wins on paying users. Rank videos on the deeper metric once you have the data.
Creator content for app installs
App ads lean heavily on creator videos because a person using the app on screen explains it faster than a feature list. Strong formats include screen recordings with a face in the corner, before-and-after results, and a creator reacting to what the app did for them. Our collection of UGC ad examples shows these formats in practice.
Brief creators on the user you want to attract, not only on features, and ask for several hooks per video so the media buyer can find the version that installs well and retains.
How it's used
The new creator batch has a CPI of 1.90 dollars, but cost per trial is up, so the installs are lower quality.
Report CPI from the measurement partner, not the ad platform, so iOS and Android are counted the same way.