Scroll Depth
A measurement of how far a user scrolls through a page or content container during a session.
Scroll depth shows whether visitors reach key content, calls to action and forms, helping teams decide where to place offers, how long pages should be and which content holds attention.
A marketing team tracks scroll at 25%, 50%, 75% and 90% thresholds in Google Tag Manager and finds only 30% of visitors reach a pricing call to action placed at 75% depth, so it moves the call to action higher.
Reaching a depth does not mean the content was read, and short pages inflate completion rates. Percentage thresholds mean different amounts of content on different devices, and GA4's default scroll event fires only at 90%.
Scroll depth is usually reported as the share of page views or sessions that reached a given threshold, calculated as sessions reaching that depth divided by total sessions on the page. GA4 enhanced measurement sends a scroll event when 90% of the vertical page height becomes visible; custom thresholds need a Tag Manager scroll depth trigger. Heatmap tools show continuous scroll reach across the page.
Data Engineering, Search Optimization
Google Analytics Help — Enhanced measurement events — https://support.google.com/analytics/answer/9216061; Nielsen Norman Group — Scrolling and Attention — https://www.nngroup.com/articles/scrolling-and-attention/