When sessions don't add up

Nothing is broken. Each row counts the sessions that viewed that page. A visit that goes Home → product → Home lands in two rows, so the sum counts it twice. The Total counts every session once.

Whether you can add the rows together depends on the dimension:

• Yes when a session has only one value, like its device or the channel it came from.
• No when the value can change during the session, like the page or the event.

The gap isn't small. In Google's GA4 sample of the Merchandise Store, 333,683 sessions viewed at least one page between November 2020 and January 2021. The rows of a report by page add up to 884,352.

Use that sum in a conversion rate and the rate drops to less than half of the real one.

Users work the same way. Someone who views five different pages sits in five rows, so a report by page counts them five times.

In the GA4 interface, even the device rows may not add up exactly to the Total, because GA4 estimates sessions and users instead of counting them one by one. That gap is tiny, nothing like this one.

To compare pages, use Views instead. Each view belongs to one page only, so the rows of Views can be added together.

Data: Google's GA4 sample from the Merchandise Store, November 2020 to January 2021, exact counts from BigQuery.