What is the Session Key Event Rate in GA4 (Google Analytics 4)?

The GA4 Session key event rate is the percentage of sessions in which one or more key events were triggered.

Following is the formula to calculate the Session key event rate:

Session key event rate = Number of sessions in which one or more key events were triggered in a particular time period / total number of sessions recorded in the same time period.

For example, 

Suppose the number of sessions in which one or more key events were triggered in the last 30 days = 50

The total number of sessions recorded in the last 30 days = 1000

Then, the Session key event rate would be calculated as = 50 / 1000 = 5%

Note: Once you have set up conversion tracking in your GA4 property, the ‘Session key event rate’ metric is populated automatically in your GA4 reports.

The ‘Session key event rate’ metric has session scope.

The ‘Session key event rate’ metric has session scope. 

This means this metric is calculated only once per session, regardless of how many times the key event might occur within the session.

Imagine you are analyzing data for your online store and want to understand how often sessions on your website lead to a ‘newsletter signup’, ‘ file download’, or ‘purchase’.

You have set the ‘newsletter signup’, file download’ and ‘purchase’ events as key events in GA4.

Scenario:

• In one day, your website recorded 1000 sessions.
• In 20 of those sessions, at least one purchase is made. In 10 of those 20 sessions with purchases, multiple purchases were made.
• In 25 out of 1000 sessions, users signed up for your newsletter. 
• In 5 out of 1000 sessions, users downloaded a file on your website.
• There are no sessions in which 2 or more key events were of different conversion types. 

Calculation of ‘Session key event rate’:

The ‘Session key event rate’ metric focuses on whether each unique session triggered a key event and not on the number of key events per session or the type of key event (‘newsletter signup’, file download’ and ‘purchase’).

So the number of sessions in which one or more key events were triggered = 20 sessions with at least one purchase + 25 sessions in which users signed up for your newsletter + 5 sessions in which users downloaded a file = 50 sessions. 

Since there are no sessions in which there are 2 or more key events of different conversion types, the number of sessions in which one or more key events were triggered = 50

The Session key event rate is calculated as  = 50 / 1000 = 5%

Now consider another scenario: 

• In one day, your website recorded 1000 sessions.
• In 20 of those sessions, at least one purchase is made. 
• In 10 of those 20 sessions with purchases, multiple purchases were made.
• In 15 of those 20 sessions with purchases, users signed up for your newsletter.
• In 25 out of 1000 sessions, users signed up for your newsletter. 
• In 5 out of those 25 sessions with signups, users downloaded a file on your website.

To calculate the Session key event rate in this scenario, we need to identify the total number of unique sessions in which at least one key event was triggered. 

The key difference in this scenario is the overlap between sessions with different types of key events.

First, calculate the number of unique sessions with one or more key events. 

20 sessions with purchases (including those with newsletter signups and potentially those with file downloads, given the data).

Given that 15 out of 25 newsletter signup sessions are already counted among the purchase sessions, we have 10 sessions that are unique to newsletter signups not accounted for in the purchase sessions.

All file download activities were accounted for within the newsletter signup sessions.

So, we have:

• 20 sessions (purchases, including those with signups and downloads)
• 10 additional sessions (unique newsletter signups)

For a total of 20 + 10 = 30 unique sessions with at least one key event. 

Therefore, the Session key event rate is calculated as:

(30/1000) × 100 = 3%

How to find and use the GA4 Session key event rate metrics

Let’s calculate the Session key event rate for default channel groups in GA4:

Follow the steps below

Step-1: Navigate to ‘Explore’ in your GA4 property:

Step-2: Click on the ‘BLANK’ report template to create a new exploration report from scratch.

Step-3: Name your report ‘Session key event rate – default channel group’:

Step-4: Import the following dimension and metric to your report: 

Dimension – Session default channel group

Metric – Session key event rate

Step-5: Double-click on the dimension ‘Session default channel group’ to add it to the canvas on the right. Similarly, double-click on the metric ‘Session key event rate’ to add it to the canvas on the right. 

Your screen should now look like the one below:

That’s how you can use the ‘Session key event rate’ metric.