Guide 172 · Conversions · GA4 + Tag Manager
Session key event rate in GA4: the formula, and why it is not the key event count
Session key event rate answers one question: in how many visits did the thing happen at least once. It is sessions with a key event divided by sessions, and it is a share, not a count. This guide computes it for a week, shows the two numbers that feed it, and works out how far the rate moves when 40 more sessions convert.
After the steps, the generate_lead 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 generate_lead key-event reference (JSON) (805 bytes, MD5 5414b0ecf7f2aa4a3a97683392c9c56d). 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, so the numerator exists. In this guide the marked event is generate_lead.
- The sessions total for the same date range as the numerator. A rate built from two different date ranges is not a rate at all.
The trace
- Open Reports, then Acquisition, then Traffic acquisition. The table carries both numbers the rate needs: Sessions, and Sessions with key events.
- Read the two numbers for the same row and the same dates. In the worked example the week shows 1,600 sessions and 192 sessions with a key event. Both numbers come from the same total row.
- Divide the sessions with a key event by the sessions. 192 / 1,600 = 12.00%. That is the session key event rate for the week. The key events count for the same week is 231, which is a different number and must not be divided by sessions in its place.
- Check the arithmetic against a second channel. The organic row shows 640 sessions and 96 sessions with a key event, which is 96 / 640 = 15.00%. If the two channels do not each divide cleanly, the total row is the one to trust.
- Test how sensitive the rate is. If 40 more of the 1,600 sessions had produced a key event, the numerator becomes 232 and the rate becomes 232 / 1,600 = 14.50%. A rise of 2.50 percentage points from 40 sessions shows how quickly a small site's rate moves.
- Quote the rate with its denominator. Write "12.00% of 1,600 sessions" rather than "12%" on its own. A rate from 1,600 sessions and a rate from 160 sessions are not equally solid, and the reader needs the denominator to tell them apart.
Dead ends
DEAD END — DIVIDING KEY EVENTS BY SESSIONS. Key events divided by sessions is events per session, not the session key event rate. On a week with repeat buyers the two differ, and the events-per-session figure is always the larger one.
DEAD END — COMPARING RATES FROM DIFFERENT DATE RANGES. A 7-day rate and a 28-day rate for the same property are not comparable without the denominators. Weekends, campaigns, and a single busy day all move a short-window rate more than a long one.
DEAD END — READING A RISE AS MORE BUYERS. The rate can rise because sessions fell while converting sessions held steady. Check the sessions total beside the rate before claiming the site converted better.
End state
The week closes at a session key event rate of 12.00% on 1,600 sessions, with 192 sessions holding at least one key event and 231 key events in total.
| Figure | Value |
|---|---|
| Sessions in the week | 1,600 |
| Sessions with at least one key event | 192 |
| Key events in the week | 231 |
| Session key event rate | 12.00% |
| Organic sessions | 640 |
| Organic sessions with a key event | 96 |
| Organic session key event rate | 15.00% |
| Rate if 40 more sessions converted | 14.50% |
The week rate is 192 / 1,600 = 12.00%, the organic rate is 96 / 640 = 15.00%, and the sensitivity check is 232 / 1,600 = 14.50%, all 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. Session key event rate as sessions with a key event divided by sessions is as Google documents it in the dimensions and metrics reference. 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.