Google Analytics 4 (GA4) is replacing Universal Analytics (GA3). To prepare everyone for the change, I’ve created a series of blog posts to help users understand the difference between the two versions. Today I’m going to walk through how time is measured in GA3 with the average session duration and average time on page metrics and compare that to how time is measured in GA4 with the average session duration and average engagement time per session metrics.
Measuring Time in GA3
With Universal Analytics (GA3), the average time on page and average session duration metrics were wildly inaccurate. This is because time measurement in GA3 was inherently flawed. Instead of collecting timestamps intermittently throughout a session, a timestamp was only recorded with a pageview. To calculate the average time on page metric, Google would subtract the time you visited page 1 from the time you visited page 2. The inherent flaw was that Google Analytics had no way of measuring the time someone spent on your exit page because there was no subsequent pageview from which to subtract.
Now, many marketers are big-picture thinkers. Sure, the number may not have been 100% accurate, but it gave us a starting point, right? Wrong. Numerous blog articles go into this in-depth, providing real-life examples, but it took a metaphor before I truly understood how inaccurate and misleading GA3 time metrics could be.
The way Google Analytics measured time in GA3 was similar to measuring the distance it takes to get somewhere using stoplights. While most of us encounter stoplights when we drive, think about the exceptions to the rule. For example, this method doesn’t account for highways, which don’t have stoplights. It also doesn’t account for the time it takes you to drive to a business that’s located right off the highway. It also doesn’t account for the fact that sometimes you’re driving across the state (or across several states for my non-Texan readers). Below is a graphic that measures the time to get from Houston to the DFW airport realistically vs. using GA3’s time measurement logic.
Measuring Time in GA4
Measuring time in GA4 is leaps and bounds more accurate. Not only is a timestamp sent with every pageview, but it’s also sent with each event that occurs. And with GA4’s out-of-the-box events, such as outbound links, file downloads, and form fills, you’re already halfway to a more accurate measure of time.
Even beyond the events you can configure for your GA4 property, Google sends some automatic events. One of these automatic events is a user_engagement event that is dispatched with the page onunload event. This means that Google Analytics understands if a user closes their browser or navigates away from the page, giving us another layer of insight into how users engage with your website that was never available in GA3.
Now let’s compare the two with real numbers. In GA3, if someone opened your webpage, browsed for 1 minute, then spent 30 minutes on another website before coming back to your website and visiting a second page. After 10 minutes on the second page, they exit the website. With GA3, their average session duration and their average time on page would be 31 minutes. In GA4, the session engagement time (the time your website was in the foreground) would be 1 minute and the average session duration would be 11 minutes (1 minute on the first page, plus 10 minutes on the second page).
Below is a comparison of the two time-based metrics in Universal Analytics (GA3) compared to GA4’s time metrics. GA4 released the average session duration metric on November 29, 2022.
| Average Time on Page | Average Session Duration | Average Engagement Time | Average Session Duration |
|---|---|---|---|
| GA3 | GA3 | GA4 | GA4 |
| The timestamp of one pageview, subtracted from the timestamp of the subsequent pageview. If there is no subsequent pageview, the time on page will be measured as 0. | The average duration (in seconds) of users’ sessions, regardless if your webpage is in the foreground or background. This excludes the time on page for the last visited webpage. | The average time that your webpage is in the foreground. | The average duration (in seconds) of users’ sessions, measured from the initial session start to the unload event. |
Based on the differences in measurement, it is highly likely that your average session duration will increase when you switch to GA4 due to the underreporting in GA3. As such, I highly recommend you don’t compare the two numbers.
Summary
Time measurement is another major upgrade you can expect from GA4, giving you more insight into which content actually engages users. GA4 is continuously rolling out new features. Learn more about GA4 reporting metrics with the blog articles below: