What Is Cumulative Layout Shift (CLS): Understanding Google’s User Experience Metric

Cumulative Layout Shift (CLS) is a vital user experience (UX) metric introduced by Google as part of its Core Web Vitals initiative. As website owners and developers strive to create better experiences for their users, understanding and optimising CLS can make a significant difference. In this article, we’ll explore what CLS is, why it matters, and how you can improve your website’s CLS score.

What is Cumulative Layout Shift (CLS)?

Cumulative Layout Shift measures the visual stability of a web page. In simple terms, it quantifies how much elements on a page shift unexpectedly during the loading process. An unstable layout can lead to a frustrating user experience, as users may accidentally click on the wrong elements or struggle to read content that keeps moving.

CLS is calculated by considering the impact of layout shifts on the viewport (visible area of the page). Higher CLS scores indicate a less stable layout, whereas lower scores suggest a more stable and user-friendly experience.

Why CLS Matters

CLS is essential for several reasons:

1. User Experience: A stable layout ensures that users can interact with a page without unexpected disruptions, leading to a more enjoyable and efficient browsing experience.
2. Conversion Rates: Unstable layouts can cause users to abandon a site, leading to lower conversion rates and potentially harming your business.
3. SEO Impact: As part of Google’s Core Web Vitals, CLS now influences search engine rankings. Websites with poor CLS scores may suffer in organic search results.

How to Improve Your Website’s CLS Score

Improving your website’s CLS score involves identifying and addressing the causes of layout shifts. Here are some strategies to help you achieve a more stable layout:

1. Reserve Space for Images and Media: Set width and height attributes for images, videos, and other media elements to prevent them from causing layout shifts as they load.
2. Avoid Inserting Content Above Existing Content: When adding new elements to a page, avoid pushing down existing content. Instead, insert new content below or in designated areas to maintain a stable layout.
3. Use Web Fonts Responsibly: Web fonts can cause layout shifts when they’re swapped with fallback fonts during loading. To minimise this, consider using the font-display property or preload key web fonts.
4. Optimise Ads and Embeds: Ads and third-party embeds can cause layout shifts if not handled correctly. Set a fixed size for ad slots and use placeholders for embedded content to prevent unexpected shifts.
5. Minimise Animations and Transitions: Animations and transitions can cause layout shifts if not used with care. Limit their use or ensure they don’t affect surrounding content.

Need Help With CLS Scores?

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Conclusion

Cumulative Layout Shift (CLS) is a critical metric for evaluating the visual stability of a website. By understanding its importance and implementing the strategies outlined above, you can improve your website’s CLS score, enhance user experience, and potentially boost your search engine rankings. Take the time to analyse your website’s performance, address any layout instability issues, and provide your users with a seamless browsing experience.