CPI
Also: Cost Per Install
CPI (cost per install) is ad spend divided by the number of installs the ads produced. It is the most-quoted mobile UA metric and, on its own, one of the least useful.
CPI = Ad spend ÷ Attributed installs
CPI varies enormously by platform, geo, and category, so a low CPI is not a good CPI unless the users retain and pay. The metric that decides whether a campaign is working is CPI against LTV per customer at a fixed window, or equivalently cohort ROAS.
Networks with cheap installs and weak retention routinely look best on CPI and worst on D30 ROAS. Report both, always.
Common mistake
Optimizing to lowest CPI. It rewards low-intent traffic and incentivized installs.
Related terms
In Roasy
Roasy computes this across every ad network, Adjust, and RevenueCat on one screen — real revenue, cohort windows, and the same definition everywhere.