CPI

CPI is the amount spent to generate one app install, the primary buying metric for mobile user acquisition.

CPI is a volume metric, and mobile UA teams that optimize purely for low CPI usually end up with a lot of low-intent installers who open the app once and never return. The install itself creates no revenue — it just buys you a shot at retention and monetization. A ₹40 CPI with 5% Day-30 retention can be worse than a ₹100 CPI with 25% Day-30 retention.

Google App Campaigns (UAC) and Apple Search Ads both push advertisers toward using CPI mainly in the early, signal-gathering phase of a campaign, then shifting bidding to a downstream event (a purchase, a subscription, a tROAS target) once there's enough conversion volume to optimize against something that actually correlates with revenue.