Scroll depth
Scroll depth is how far down a page users actually scroll, usually expressed as a percentage of page height or as reach past defined milestones. It measures exposure: content below the typical maximum scroll depth was never seen, regardless of what click metrics say about it.
How it works
Replay-based measurement derives depth from recorded scroll events (source: 3) combined with viewport size from meta and resize events, computing the furthest visible point per session. The events documentation lists the source values used by these events. Aggregated across sessions, it yields the classic fold curve: what fraction of visitors saw each region of the page. Session data adds what page-level analytics miss, such as scroll velocity (skimming versus reading) and backtracking (scrolling up to re-find something), both of which carry meaning about comprehension rather than mere exposure.
Where you encounter it
Landing page and content optimization, placement decisions for calls to action, and diagnosis of long-form pages; pairs naturally with heatmap views and conversion analysis.