What is a Session?

A session is a continuous series of interactions by one user on a website within a certain period of time. In Google Analytics 4, a session starts with the first pageview or event and ends after 30 minutes of inactivity (you can change this timeout in the GA4 settings).

Session versus user

One unique visitor (user) can generate several sessions. Someone who visits your website on Monday and Thursday counts as one user but two sessions. Sessions measure visit frequency; users measure the number of unique people.

Sessions in GA4

GA4 calculates sessions on an event basis through the session_start event. This differs from Universal Analytics, which was page based. Because of this difference, session counts in GA4 can differ from the old Universal Analytics data.

Measuring session quality

Combine sessions with bounce rate, session duration and pageviews per session for a full picture of traffic quality. A high number of sessions with a high bounce rate points to irrelevant or poorly targeted traffic.

What is session duration?

The time between the first and last event in a session. GA4 measures this more accurately through engagement time than the time on page measurement in Universal Analytics.

Does coming straight back count as a new session?

Yes, after 30 minutes of inactivity a new session starts automatically on the next visit. More at developers.google.com/search.