CPI, stands for Cost per Install, is a commonly used pricing model in mobile user acquisition campaigns where mobile advertisers are charged every time a user installs a mobile app by clicking an ad. It indicates how much money an app advertiser needs to acquire a user who installs the app.

CPI is highly affected by the other elements of the advertising campaign, including the quality of creatives, countries the campaign is run, the demographics of the target audience, and the app category. 

CPI= Advertising Cost / Number of App Installs from a Specific Campaign