The essentials
- Definition: a session groups a visitor's interactions over a period, closing after 30 minutes of inactivity.
- Engaged session: more than 10 seconds, or a key event, or at least 2 page views. The basis of the engagement rate.
- What changed: no more new session at midnight or when the campaign changes, so you get fewer sessions than with Universal Analytics.
- Session ≠ user: one user can generate several sessions; 2,000 sessions for 1,400 users is a common ratio.
In Google Analytics 4, a session means a visit: the period during which one visitor interacts with your site. It begins with the session_startevent, fired automatically, and ends after 30 minutes with no interaction. It is the most used metric in acquisition reports, and one of the most misunderstood.
How GA4 defines a session
GA4 assigns a session ID to the first event of a visit. Every subsequent event from the same visitor attaches to it as long as it happens within 30 minutes of the previous one. A few rules worth knowing:
- The inactivity timeout can be set from 5 minutes to 7 hours in the data stream settings, but 30 minutes remains the norm.
- A session can run past midnight; GA4 doesn't cut it, unlike Universal Analytics.
- A visitor returning through another campaign during an ongoing session does not create a new session. The session's source stays the one from its first event.
- A session doesn't necessarily contain a page view: a single isolated event (an interrupted load, say) is enough to create one. That's where the "(not set)" rows under landing page come from.
Session, engaged session, user: the table
| Metric | Definition | Use |
|---|---|---|
| Sessions | Number of visits ( session_start) | Compare volume by channel, campaign, landing page |
| Engaged sessions | Sessions lasting more than 10s, or with a key event, or with at least 2 page views | Measure traffic quality |
| Engagement rate | Engaged sessions / sessions | Replaces bounce rate (its inverse) |
| Active users | Distinct visitors who had at least one engaged session | Measure your audience |
| Sessions per user | Sessions / active users | Measure loyalty (generally 1.2 to 1.6) |
| Average engagement time per session | Time the page spent in the foreground / sessions | Judge how interesting your content is |
What changes compared with Universal Analytics
If your GA4 sessions look 10 to 20% lower than the old figures, that's normal. Universal Analytics created a new session at midnight and on every change of source or campaign. GA4 no longer does. Conversely, GA4 counts sessions with no page view that Universal Analytics ignored. The full comparison is in GA4 vs Universal Analytics.
Another difference: duration. Universal Analytics calculated the time between the first and last hit, which gave single-page visits 0 seconds. GA4 measures the real time the tab spent in the foreground, through the user_engagementevent. Durations are therefore shorter but more accurate.
Why the session matters for running your marketing
The session is the unit of measurement for acquisition. When you compare SEO and Google Ads, you are comparing sessions: how many, their engagement rate, their conversion rate. Three concrete uses:
- The conversion rate per session (key events / sessions) is the KPI that lets you compare channels of different sizes. See GA4 KPIs.
- The engagement rate by channel reveals the sources sending you visitors with little interest: a social campaign at 25% engagement when SEO is at 65% deserves a rethink of its targeting.
- Sessions by landing page are the best way to read SEO in GA4, cross-referenced with Search Console rankings.
Traps when reading the data
- Adding up sessions from several properties or comparing them with another tool (Matomo, server-side): each tool has its own definition.
- Taking sessions for people. 1,000 sessions can come from 600 people.
- Forgetting consent. Sessions from visitors who refuse cookies aren't counted (or only modelled, with Consent Mode). A drop in sessions can come from a change to your banner, not from traffic.
- Payment referrers. Without excluding Stripe or PayPal from your referrals, every return from payment can open a new session attributed to the payment provider. See setting GA4 up properly.
How GreenRed helps
Rather than juggling several tools, GreenRed's Traffic module brings these metrics together in a single dashboard, compares them over time and tells you which actions come first. You can try it free, with no card, from the Pricing.
Frequently asked questions
How long does a GA4 session last?
As long as the visitor keeps interacting, with a cut-off after 30 minutes without an event. That timeout can be changed (from 5 minutes to 7 hours) in the data stream settings, but changing it is inadvisable: your data would no longer be comparable with other sites' or with your own history.
Why do I have fewer sessions in GA4 than in Universal Analytics?
GA4 no longer creates a new session at midnight, nor when a visitor returns through another campaign during an active session. Those two changes cut session counts by 10 to 20% depending on the site, without real traffic having fallen at all.
What is the difference between a session and an engaged session?
An engaged session is one that lasted more than 10 seconds, or contains a key event, or at least two page views. The ratio between the two gives the engagement rate, which replaced bounce rate. A rate of 60% means 40% of visits ended almost immediately.
Can a session have several sources?
No. GA4 attributes the session to the source of its first event. If a visitor arrives from Google, then clicks an email within 30 minutes, the session stays attributed to Google. The user, on the other hand, keeps their first acquisition source in the "User acquisition" reports.