# What is CLS (Cumulative Layout Shift)?

> CLS measures how much a page's content unexpectedly jumps around while it loads; Google rates a score of 0.1 or less as good.

- Source: https://nerdsharks.com/glossary/cls
- Publisher: Nerdsharks (Exeter, Devon, UK)
- Updated: 2026-09-26

Also called: Cumulative Layout Shift, layout shift, visual stability.

Cumulative Layout Shift is the Core Web Vital for visual stability. You have seen the problem: you go to tap a link, an image or banner loads above it, everything moves down, and you tap the wrong thing.

CLS is a score rather than a time. Google's thresholds: 0.1 or less is good, up to 0.25 needs improvement, and above 0.25 is poor.

Common causes are images without set dimensions, adverts or cookie banners that push content down, and fonts that load late and change the size of text.

## Why it matters for a small business

A jumping page is irritating at best, and at worst it means someone taps ‘Call’ and hits something else. It makes a site feel cheap and unreliable, and it is usually easy to fix once someone looks for it.

**Example:** On a plumber's site, a promotional banner loads a moment late and shoves the phone number down just as the visitor goes to tap it. Reserving space for the banner fixes it.