Session

Definition

A session represents a period of continuous interaction between a user and a website or application. It is a fundamental unit of measurement in web analytics that groups a visitor’s actions into a single coherent visit.

How it works in GA4

In GA4, a session starts automatically with the event session_start. It ends after 30 minutes of inactivity (configurable up to 7 hours). Unlike Universal Analytics, a change in traffic source during navigation does not trigger a new session in GA4.

Each session receives a unique identifier (ga_session_id) that links all events within the same visit. The session number (ga_session_number) indicates how many times the user has returned to the site.

Associated metrics

Sessions feed several key metrics: total session count, engaged sessions (over 10 seconds, 2+ page views or 1+ conversion), engagement rate and average session duration. These indicators are essential for evaluating traffic quality by acquisition channel.

Importance for analysis

Session counting depends directly on the quality of the tracking in place. A missing first-party cookie or refused consent can create artificially fragmented sessions, distorting the analysis. A tracking audit helps identify these issues.