GA session number dimension
The GA session number dimension records the ordinal of the current session for a user — 1 for their first ever session, 2 for the second, and so on. GA4 derives it from the ga_session_number event parameter, incremented per device/client identity. It is the basis for engagement-by-visit analysis, but it resets whenever the underlying identifier is cleared, so consent and cookie loss inflate the count of session number 1.
What this means
GA session number is the count of sessions GA4 has recorded for the current user identity, exposed via the ga_session_number parameter the SDK sets on each session_start. The first session is 1; each subsequent session increments it.
It powers questions like 'do second-visit users convert more than first-visit users?' by slicing reports along the visit ordinal.
Why it resets
Session number is tied to the client/device identifier. If that identifier is cleared — cookie deletion, a new device, denied analytics consent — GA4 sees a new identity and the counter restarts at 1. So an unexpectedly high share of session number 1 often reflects identity churn rather than genuine new visitors. Interpret it alongside new-vs-returning and consent context.
- Derived from the ga_session_number parameter
- 1 = first session for the current identity
- Resets when the underlying identifier is lost
How it appears in analytics and logs
A session number of 1 marks a first session for that identity. A spike in session number 1 can indicate identity loss (cleared cookies, denied consent), not a surge of new people.
Diagnostic use case
Use session number to study how behaviour changes across a user's first, second, and later visits, or to isolate first-ever sessions.
What WebmasterID can help detect
WebmasterID can reason about visit ordinality from first-party signals while remaining honest that cleared identity legitimately resets the counter.
Common mistakes
- Reading every session number 1 as a brand-new person.
- Ignoring consent/cookie loss when the counter resets.
- Confusing session number with total session count.
Privacy and accuracy notes
Session number is derived per device/client identifier, not a cross-site profile. When identity is reset, the count restarts — a privacy-preserving side effect, not a defect.
Related pages
- New vs returning dimension
The new vs returning dimension classifies a visitor as new (no prior recorded visit) or returning. The classification depends on a persistent client identifier surviving between visits. When cookies or storage are cleared, browsers cap identifier lifetime, or a user switches devices, returning visitors are recounted as new — so this dimension systematically tilts toward 'new' and should be read with that bias in mind.
- Days since last session dimension
The days since last session dimension reports how many days have elapsed since the user's previous session. GA4 computes it from the stored last-session timestamp on the current identity. It supports recency and re-engagement analysis, but it can only be calculated when GA4 still recognises the user — if the identifier was cleared, the prior session is invisible and the return is counted as new, so the gap is undercounted.
- New vs returning misclassification
New-vs-returning depends on recognising the same visitor across visits, which relies on a stored identifier. When that identifier is missing — cleared cookies, tracking prevention, a different device or browser, or declined consent — a returning visitor is recorded as new. The result over-states 'new' visitors and understates loyalty. This page explains the failure modes.
- Privacy-first analytics
Visit ordinality without cross-site profiling.
Sources and verification notes
- Google — [GA4] Automatically collected events (ga_session_number)
- Google Analytics for Firebase — Automatically collected events
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.