eCPI stands for Effective Cost Per Install. It is a metric used in mobile advertising campaigns, particularly in app marketing, to measure the cost-effectiveness of acquiring new users. The eCPI represents the average cost incurred to generate a single app installation or download. 

The calculation of eCPI involves dividing the total cost of an advertising campaign by the number of app installs attributed to that campaign.  

The formula 

eCPI = Total Cost / Number of Installs 

For example, if a mobile advertising campaign costs $1,000 and generates 500 app installs, the eCPI would be $2 ($1,000 / 500 = $2). This means that, on average, each app installation in that campaign cost $2. 

eCPI is a valuable metric for app marketers as it allows them to evaluate the efficiency and profitability of their user acquisition efforts. By comparing eCPI across different campaigns or advertising channels, marketers can determine which sources provide the most cost-effective installations and allocate their budgets accordingly. Lower eCPI indicates more efficient user acquisition, while higher eCPI may warrant further optimization or reevaluation of the advertising strategy.