# Cumulative Layout Shift (CLS) | SEO Glossary

> Cumulative Layout Shift (CLS) explained in plain English. Understand what cumulative layout shift (cls) means, why it matters for SEO, and how it works.

**Source:** https://www.lawrencehitches.com/glossary/cumulative-layout-shift-cls/

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Breadcrumb Category tag Technical Seo H1

# Cumulative Layout Shift (CLS)

Definition block A Core Web Vital that measures unexpected visual movement on a page as it loads. It quantifies how much content shifts around without user interaction. Google considers a score under 0.1 as good.

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Expanded explanation

## Why Cumulative Layout Shift (CLS) Matters for SEO

Layout shifts are the reason you accidentally click the wrong button when a page jumps around. Beyond annoying users, poor CLS scores hurt your Core Web Vitals assessment and can contribute to higher bounce rates, especially on mobile.

## How Cumulative Layout Shift (CLS) Works

The browser calculates a shift score based on the size of the shifting element and how far it moved. Every time an element moves without user input, the score increases. Common causes are images without dimensions, ads injecting above content, and web fonts swapping in with different sizes.

## Common Mistakes

- Not setting explicit width and height on images and video embeds
- Injecting dynamic ad slots that push content down after initial load
- Using font-display: swap without matching fallback font metrics

Video (if available) Article link (if exists) Want to go deeper? Read the full guide: Core Web Vitals → External sources Sources & Further Reading:

- [web.dev: Cumulative Layout Shift (CLS)](https://web.dev/articles/cls)
- [web.dev: Optimize Cumulative Layout Shift](https://web.dev/articles/optimize-cls)

Related articles Related terms Author bio About the Author

Lawrence Hitches is an [AI SEO consultant based in Melbourne](https://www.lawrencehitches.com/) and Chief of Staff at StudioHawk. He specialises in AI search visibility, technical SEO, and organic growth strategy. [Book a free consultation →](https://www.lawrencehitches.com/contact/)

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*Lawrence Hitches is an AI SEO consultant in Melbourne and Chief of Staff at StudioHawk, Australia's most awarded SEO agency. Agent edition of this site: https://www.lawrencehitches.com/md/index.md*