Scroll depth

Scroll depth measures how far down a page a visitor scrolls, usually reported as the percentage of the page height reached or as discrete thresholds, such as 25%, 50%, 75%, 90% and 100%. It is tracked with JavaScript that fires an event each time a visitor's scroll position crosses a configured threshold; several analytics platforms track a 90% scroll threshold automatically as part of default event collection.

Scroll depth differs from pageview or average session duration in that it measures how much of the content was actually exposed to the visitor, not just that the page loaded or that time passed — a tab left open in the background accrues session time without anyone reading a word. It is often analyzed alongside a heatmap's scroll-map view, which shows the same information visually as a fold line across many aggregated visits rather than as a single percentage.

Scroll depth is used to judge whether content below the first screen is actually being seen — important for long-form articles, product pages with specifications further down, or pages where a call to action sits past the fold. The main pitfall is treating scroll depth as proof of reading: a visitor can scroll quickly to the bottom of a page without absorbing anything in between, so scroll depth is a proxy for exposure, not comprehension, and is best paired with content engagement signals like time-in-view.