Users, sessions and engagement

A user in GA4 is identified by a pseudonymous ID stored in the _ga cookie (or by your own User-ID; see reporting identity). GA4 reports three user metrics: Total users (anyone who logged an event), New users (fired first_visit), and Active users, which is what the plain "Users" column in standard reports means. A user is active if they had an engaged session or their first visit in the period.

A session starts with the automatic session_start event and ends after 30 minutes of inactivity (adjustable between 5 minutes and 7 hours 55 minutes in the web stream's tag settings). Unlike Universal Analytics, a session does not restart at midnight or when a new campaign parameter appears, so GA4 usually shows fewer sessions than UA did for the same site. Every event carries ga_session_id so GA4 can group them.

A session is engaged when at least one of these is true:

• it lasted longer than 10 seconds (adjustable up to 60 seconds in tag settings),
• it had a key event,
• it had two or more page views or screen views.

Engagement rate = engaged sessions / sessions. Bounce rate still exists but is simply 1 minus engagement rate. Average engagement time comes from the user_engagement event, which the tag sends with the time the page was actually in the foreground, so it is more honest than UA's time on page.

Views per session and Sessions per user round out the basic set. Because engagement is measured client-side, a user who reads a page for 2 minutes and leaves counts as engaged, which UA would have called a bounce.