Guide 171 · Conversions · GA4 + Tag Manager
Sessions with key events in GA4: what the metric counts, and how to read it
Sessions with key events is a session count, not an event count. A session with five purchases still counts as one session with a key event. This guide reads the metric in the Traffic acquisition report, shows how it differs from the key events count, and works out both numbers for the same week so the gap is visible.
After the steps, the purchase key event appears under the Key events tab in Admin, and the standard reports show it within a day. The worked example below gives the count and the rate to expect.
Download the reference: the purchase key-event reference (JSON) (679 bytes, MD5 c6a9a1539ce39f780d10c15940405b07). It holds the event name, the counting method, the worked-example figures recomputed for this guide, and the checkpoints that prove the key event is recording. The figures in the file are the same figures shown on this page.
What you need
- Editor access or above at property level in GA4. Marking an event as a key event is a property setting, and the star in the Events table does not appear for a Viewer.
- At least one key event marked in the property, so the metric has a numerator. In this guide the marked events are purchase and generate_lead.
- A date range long enough to compare. The worked example uses 28 days, which is long enough that a single busy day cannot hide the pattern.
The trace
- Open Reports, then Acquisition, then Traffic acquisition. The table shows sessions by channel, with a Key events column and a Sessions with key events column beside it.
- Read the Sessions with key events column first. It counts sessions in which at least one key event happened. A session with five purchases counts once here, even though it counts five times in the Key events column.
- Compare it with the Key events column on the same row. In the worked example the week shows 412 key events across 2,500 sessions, but only 338 sessions with a key event. The gap of 74 is repeat key events inside sessions that already counted.
- Check the total row, not just one channel. The total row gives the property-wide count. In the worked example the total is 338 sessions with a key event out of 2,500 sessions.
- Add the metric to a report that lacks it. In a standard report, use the customize control to add Sessions with key events as a metric. It is a session-scoped metric, so it pairs with session dimensions such as Session source / medium, not with event names.
- Use it as the numerator of the rate. Session key event rate is this metric divided by sessions: 338 / 2,500 = 13.52%. The rate is covered in its own guide; this guide is only about the count.
Dead ends
DEAD END — READING KEY EVENTS AS SESSIONS. The Key events column counts events, and the Sessions with key events column counts sessions. On a week with repeat buyers the two numbers differ by the repeat count, and quoting the event count as if it were visits overstates reach.
DEAD END — PAIRING A SESSION METRIC WITH AN EVENT DIMENSION. Sessions with key events beside Event name gives a number that does not mean what the label suggests, because the scopes do not match. Keep session metrics with session dimensions.
DEAD END — EXPECTING THE COUNT TO MATCH THE USER COUNT. One user can have several sessions in a week, and each session with a key event counts. Sessions with key events is usually larger than users with a key event, and the two are different metrics.
End state
The week closes at 338 sessions with a key event out of 2,500 sessions, against 412 key events in total. The gap is repeats inside sessions that already counted.
| Figure | Value |
|---|---|
| Sessions in the week | 2,500 |
| Key events in the week | 412 |
| Sessions with at least one key event | 338 |
| Repeat key events inside counted sessions | 74 |
| Session key event rate | 13.52% |
The gap is 412 − 338 = 74, and the rate is 338 / 2,500 = 13.52%, both recomputed in Python 3 and rounded to two places. The figures are a worked example, not a real property.
Sources
- Analytics Help — About key events — marking an event as a key event, the 30-event limit for a standard property, and 50 for Analytics 360
- Analytics Help — Conversions vs. key events in Google Analytics — what a key event is, the event to key event to conversion flow, and where Google Ads conversions appear
Checked 11 November 2026. The click path above is the one in Google's help pages, read 11 November 2026. A session with a key event counting once for the session, however many times the event fired, is as Google documents it. No step in this guide was run inside a live Analytics property, because the reports need a Google sign-in and this site does not sign in as anyone. The figures on this page are a worked example recomputed in Python 3 with decimal arithmetic, not numbers from a real property. Google moves menu items without warning; if a path on this page no longer matches, the linked help page is the current map.