Session length is the amount of time spent by a user inside your app during a session. It begins when the user launches your app and ends when they stop using your app or leave it completely.
This metric tracks how long a user was having a continuous experience in your app, and as such, serves as an indicator of user engagement.
Using session length, you can figure out if users are inside your app long enough to reach the desired milestones of purchasing a product, or sharing content (or whatever conversion goal you have). Obviously, if users aren’t staying on long enough, you have a problem that needs solving.
Note also that while session length is important, this metric will vary depending on your industry, your users, and the the type of app you are marketing.
To calculate session length, you need only subtract the time the app was launched from the time the user becomes inactive or exits the app entirely.
The formula is simply:
(Time user becomes inactive) – (Time app is launched) = Session length