A session represents a single visit to your website. It begins when a user arrives on a page and ends when they leave the site or remain inactive for a set period (typically 30 minutes). One user can generate multiple sessions — visiting in the morning and returning in the afternoon counts as two sessions.
How Sessions Are Defined
Most analytics and experimentation platforms define a session as a group of interactions that occur within a time window:
- Session starts when a user loads their first page
- Session continues as they navigate between pages and interact with content
- Session ends after 30 minutes of inactivity, at midnight, or when the user closes the browser (depending on the platform)
A single user visiting your site three times in a week generates three sessions but counts as one unique visitor.
Sessions vs. Users vs. Pageviews
| Metric | What It Counts |
|---|---|
| Session | One visit (may include multiple pageviews) |
| User (unique visitor) | One person (may have multiple sessions) |
| Pageview | One page load (many per session) |
If one person visits your site twice and views 4 pages each time, that's: 1 user, 2 sessions, 8 pageviews.
Sessions in Experimentation
In A/B testing and CRO, sessions matter because:
- Variant assignment is typically per-session or per-user — A visitor should see the same variant throughout a session to avoid confusion
- Conversion rates are often calculated per-session — "3% of sessions resulted in a signup"
- Sample size is measured in sessions — You need a certain number of sessions per variant to reach significance
Per-Session vs. Per-User Metrics
- Per-session conversion rate: What percentage of visits result in a conversion? Useful for measuring page-level performance.
- Per-user conversion rate: What percentage of unique visitors eventually convert? Useful for measuring longer buying cycles where visitors return multiple times.
Session Duration and Quality
Not all sessions are equal. Key quality indicators:
- Session duration — Longer sessions generally indicate higher engagement
- Pages per session — More pages suggest the visitor is exploring your content
- Bounce rate — The percentage of sessions where the visitor leaves after viewing only one page