Scroll Depth
BeginnerScroll depth records how far down a page a user scrolled, usually reported as the percentage of that page's total height reached.
Measurement works on thresholds: an event fires each time the viewport passes the 25, 50, 75 and 100 percent marks, and what gets reported is the deepest point reached during that view. Comparing the percentage across pages of different length misleads; hitting 100 percent on a short mobile page is nearly free, while the same number on a long article means something else. The more common error is reading depth as reading: a fast scroll to the bottom records the same 100 percent as careful reading. Page height also includes the footer, comments and recommendation blocks, so the denominator is always larger than the content itself.
How it is calculated
Scroll depth = deepest point reached in the view ÷ total page height
It is computed per page view and the result is usually bucketed into percentage thresholds rather than kept continuous; the output is a percentage and it cannot be summed or directly compared across pages of different length.