At a glance the headline numbers for Largest single shift
The single largest layout-shift score captured.
The largest single layout shift on the typical site scores 0.
Distribution & median CLS site count and median CLS at each level of largest single shift
Passing CLS by largest single shift which level passes the CLS most often
Largest single shift 0.0. p75 0.1. p99 1.0. Spearman with CLS r = +0.33. At the low end (0): CLS 0.01. At the high end (>p98): CLS 0.19. computed
Why this matters for the Core Web Vitals, and where to start fixing it
A layout shift score multiplies how much of the viewport moved by how far it moved. One full-width block jumping down can fail the CLS threshold on its own. The largest single shift tells you whether a site has that one dominant event or death by a thousand small ones.
If the largest shift carries most of the total, the work is finding one element. The usual suspects: a hero image without dimensions, a banner injected above the content, a font swap that reflows the page. Reserve the space that element needs and the problem is gone.
How does this affect the Core Web Vitals?
Largest shift is part of the CLS itself, so this is arithmetic, not correlation. 86% of sites at the low end pass the CLS. Past 0.9, the typical site fails. At the top of the range only 39% pass.
Chrome field data from 94,910 sites, representing millions of real page loads. How we measured.