CPI (Cost Per Install) is the amount you pay each time your app is installed through mobile app advertising. You are charged on a concrete outcome - the install - not on impressions or clicks. It is a core efficiency metric in app marketing.
Formula
CPI = Ad Spend ÷ Number of App Installs
For example, if 1 million KRW in ad spend drives 5,000 installs, the CPI is 200 KRW. Even with the same budget, CPI shifts significantly based on creative and targeting.
Relationship with Impression and Click Metrics
CPI is shaped by upstream metrics like Cost Per Click (CPC) and Cost Per Mille (CPM). The flow works as follows:
- Impression stage: cost accrues via CPM
- Click stage: higher CTR lowers cost per click
- Install stage: higher store conversion rate lowers CPI
In short, you must raise both creative CTR and store page conversion rate to bring CPI down.
Why It Matters
CPI is the starting point of Customer Acquisition Cost (CAC) in an app business. But an install is not the same as an active user. To measure real performance, track post-install Daily Active Users (DAU), Monthly Active Users (MAU), and retention together.
Even a low CPI leads to a loss-making structure if Lifetime Value (LTV) cannot keep pace. Always verify that the 'LTV > CAC' condition holds.
Notes
- Paid CPI faces intense price competition. Over the long term, distributing your average CAC through organic traffic built on SEO and content SEO is an effective strategy.
- 238lab designs paid ad efficiency alongside search and generative channel traffic to optimize your app acquisition cost structure.