CPA measures the average cost to acquire a user who completes a specific in-app action, providing a deeper efficiency metric than CPI.
Cost per acquisition (CPA) measures how much advertising spend is required to drive one user to complete a defined conversion event, typically an in-app purchase, subscription start, tutorial completion, or registration. Unlike CPI which counts any install, CPA measures quality acquisition: users who took the action you actually care about.
CPA is the natural next metric after CPI in the UA efficiency hierarchy. A campaign may achieve excellent CPI but poor CPA if the installs it drives don't engage or convert in-app. The gap between CPI and CPA reveals your install-to-action conversion rate and highlights where funnel optimization is needed, in the creative (pre-install) or the onboarding experience (post-install).
Platforms like Meta allow bid optimization directly toward CPA events through their conversion campaign objectives, meaning advertisers can tell the algorithm to find users likely to complete specific in-app events, not just install.
CPA aligns creative performance measurement with revenue outcomes. A creative that drives cheap installs from low-intent users will have low CPI but high CPA. The installs don't convert to actions. Evaluating creatives at the CPA level (not just CPI) tells you whether you're acquiring users who actually do something valuable inside the app.
Example
“A fitness app targets subscription starts as its CPA event. Two creatives achieve the same CPI of $3.50, but Creative A drives $12 CPA (29% install-to-subscribe rate) while Creative B drives $28 CPA (12.5% rate), making Creative A clearly superior despite equal install costs.”
Segwise Feature
Track CPA by creative with Segwise
CPI is the average amount spent in advertising to generate one app install. It's the most common efficiency metric in mobile user acquisition.
Learn moreMobile User AcquisitionROAS measures revenue generated for every dollar spent on advertising, serving as the primary efficiency metric for paid user acquisition.
Learn moreMobile User AcquisitionLTV is the total net revenue a user is expected to generate over the full course of their relationship with your app, used to determine how much you can profitably spend to acquire them.
Learn moreMobile User AcquisitionConversion rate measures the percentage of users who complete a desired action at each stage of the acquisition funnel, from impression to install to in-app event.
Learn moreConnect your ad networks and MMP in 5 minutes. AI tags every creative automatically.
Start Free Trial