Percent scrolled dimension: a coarse depth signal
Percent scrolled is the dimension that records how far down a page a visitor scrolled. GA4 enhanced measurement, by default, fires a single scroll event at the 90% depth threshold, carrying percent_scrolled. It is a coarse engagement proxy: out of the box it tells you only whether someone reached near the bottom, and scroll depth is not the same as reading or attention.
What this means
GA4 enhanced measurement includes scroll tracking. By default it fires one 'scroll' event per page when the visitor first reaches 90% vertical depth, recording percent_scrolled = 90. The percent scrolled dimension exposes that value.
It answers a narrow question: did this visitor get near the bottom of the page at least once?
Why it is coarse and easily misread
Out of the box there is only the 90% threshold — no 25/50/75% breakdown unless you implement custom scroll tracking. So the default dimension is close to binary: reached-the-bottom or not.
Even at 90%, scroll depth is not attention. A visitor can fling the scrollbar to the bottom in a second, or a short page can hit 90% with almost no content. Treat it as a weak proxy and pair it with time-based engagement before drawing conclusions.
- Default GA4 fires scroll once at 90% depth
- Finer thresholds require custom implementation
- Depth is not reading or attention
How it appears in analytics and logs
A percent_scrolled value of 90 means a visitor reached near the page bottom. The absence of finer thresholds is by design in default GA4, not missing data, and reaching 90% does not prove the content was read.
Diagnostic use case
Use percent scrolled as a rough indicator of who reaches the bottom of a page, while remembering the default is a single 90% threshold, not continuous depth.
What WebmasterID can help detect
WebmasterID can capture scroll engagement as first-party events, so depth is measurable without third-party scripts or invasive tracking.
Common mistakes
- Assuming GA4 tracks 25/50/75% scroll by default.
- Equating reaching 90% with reading the content.
- Ignoring page length when comparing scroll depth across pages.
Privacy and accuracy notes
Percent scrolled measures interaction with a page, not the person. WebmasterID records scroll engagement first-party without behavioural fingerprinting.
Related pages
- Video title dimension: which videos get watched
Video title is the dimension that records which embedded video a visitor engaged with. GA4 enhanced measurement captures it for YouTube embeds that use the IFrame Player API, firing video_start, video_progress, and video_complete with a video_title parameter. The key limit: only API-enabled YouTube players are auto-tracked — other hosts and plain embeds need manual instrumentation to populate the dimension.
- Bounce rate: definition and why it misleads
Bounce rate is the percentage of sessions with only one interaction. Its definition shifted: classic tools counted single-pageview sessions; GA4 derives it from engaged sessions instead. A high bounce rate is not inherently bad — for a single-answer page it can mean success — which is why context matters more than the number.
- The scroll event and depth tracking
A scroll event records that a visitor scrolled to a depth on the page. In GA4 enhanced measurement, a single scroll event fires once per page when the visitor reaches 90% of the page height. It is a coarse engagement signal — useful for spotting content people do not reach, but limited because the default is one threshold, not a continuous read-depth curve.
- Web analytics
Measure scroll engagement first-party.
Sources and verification notes
- Google Analytics Help — [GA4] Enhanced measurement eventsDocuments the default 90% scroll threshold and percent_scrolled.
Last reviewed 2026-06-24. Facts are checked against primary/official sources where available; uncertain specifics are marked “Data not yet verified” rather than guessed.