AnalyticsGoogle Analytics 42 min read

Key event rate per session: the GA4 definition

It's GA4's conversion rate, computed on sessions. How it differs from Google Ads' and how to read it without going wrong.

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Contents
  1. Definition
  2. Formula
  3. Worked example
  4. Orders of magnitude
  5. The most common mistakes
  6. Where to find the metric
Key takeaways
  • It's GA4's conversion rate, relative to sessions rather than ad clicks.
  • It exists in two variants, per session and per user, which give different figures for the same reality.
  • It never compares to an ad platform's conversion rate: the denominators differ.

Definition

The key event rate per session measures the proportion of sessions that triggered at least one key event.

Formula

Rate = sessions with a key event divided by total sessions, times one hundred.

Worked example

A site records 10,000 sessions and 320 sessions with a form submission, so 3.2%. Google Ads shows at the same time a 4.6% conversion rate: it computes on its clicks, not on sessions, and attributes only what follows an interaction with its ads.

Orders of magnitude

No useful reference out of context. It reads by channel: brand traffic always converts markedly better than cold acquisition, and a global average blends the two.

The most common mistakes

  • Comparing the per-session and per-user variants. One user who came three times before converting gives two very different figures.
  • Comparing it to Google Ads or Meta. The denominators and attributions don't line up.
  • Reading it across all channels. The average masks gaps from one to ten.

Where to find the metric

In GA4, the Key event rate per session and Key event rate per user metrics, available in the acquisition reports and explorations.

Frequently asked questions

Per session to judge a visit's effectiveness, per user to judge a journey spread over several visits. Both are right, they don't answer the same question.

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Editorial

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