Metrics
CPI
Cost per install — what you pay per app install.
CPI (cost per install) is the per-install payout in mobile-app user-acquisition. The default conversion event in mobile UA before the industry shifted toward CPE (cost per engagement) and ROAS targets. CPI deals are common on incentivized networks, mobile DSPs (Liftoff, Moloco, Applovin), and on offer walls. Tier-1 organic CPIs run $2–$8; gaming and finance CPIs can hit $15–$40. Postback fires on the SDK install event via MMP (AppsFlyer, Adjust, Singular).
Formula
CPI = ad spend / installs
Example
A casual game runs at a $4.50 CPI on Applovin in the US. Day-7 ROAS is 0.4×, so the campaign needs Day-30 monetization to clear breakeven.