Sessions are a basic unit of measurement for app engagement. Most app owners want their app to be so engaging, a user never puts it down. But, in order to engage with an app, a user has to launch it. Each launch counts as a session* and looking at session lengths help app owners quickly understand if users are actually using their application.
Session length is typically defined as the amount of time the app is in front of the user. There are exceptions: some apps (such as streaming audio apps) may also include time spent streaming in the background, and always-on apps (such as kiosks) may build timeouts into their session model. But in most cases, there is value in looking at the time the user spent staring at the screen.
Let’s compare two example apps to illustrate the importance of session length:
Which example app has the better engagement?
The easy answer is Example Two. Users of Example Two spend longer, on average, in the app than Example One. In fact, the bulk of Example Two’s usage is longer than three minutes whereas the bulk of Example One’s is less than three minutes. Because the session length of Example Two’s users is longer, it’s easy to assume the app is more engaging, and thus better.
But that may not be the right answer.
If the apps being compared are both content apps showing similar content, then Example Two is most likely doing a better job engaging users. But what if Example Two is a taxi finding service? I’d much rather find a Taxi in one minute than 10 minutes.
It is important for app publishers to understand whether their app’s mission is best served by keeping users in the app as long as possible or by returning them as quickly as possible, and only session length can tell them that. A media app will likely think of success in terms of time spent reading while taxi apps may want the minimum time to find you a car.
Session length is not the only metric for measuring engagement, but it is one that really matters.
*In Localytics, a session is defined as a focused use of the app, which means that if a user leaves the app and relaunches it immediately we still consider that one session. For more details see our guide on sessions.