Understanding the Critical Role of Cumulative Layout Shift (CLS) in Web Design

In the fast-evolving landscape of web design, one metric that has gained significant attention among developers and SEO experts alike is the Cumulative Layout Shift (CLS). Since it directly affects user experience, this indicator has grown in importance and is currently included in Google’s Core Web Vitals. We’ll go into great detail on what CLS is, why it matters, and how to optimize your website to raise this crucial metric in this blog post.

What is Cumulative Layout Shift (CLS)?

Cumulative Layout Shift refers to the unexpected shifting of web page elements while the page is still downloading. These shifts can occur for various reasons, such as images loading without dimensions, ads inserting dynamically, or fonts causing visible changes to text layouts. A high CLS score can be frustrating for users as it leads to a poor experience; users may click on the wrong buttons or links accidentally if elements shift under their cursor or finger.

Why Does CLS Matter?

Google has always emphasized user experience, and with the introduction of Core Web Vitals, CLS has become a pivotal factor in website ranking. Websites with a low CLS score (indicating fewer layout shifts) are considered to provide a better user experience and are thus favored in search engine results. Moreover, minimizing layout shifts is crucial for ensuring accessibility and usability, particularly for users with impairments who rely on predictability and stability on the web.

How to Measure CLS

CLS is measured by assessing the impact fraction and distance fraction of layout shifts that aren’t caused by user interactions. The impact fraction measures how much visible space an element impacts when it shifts, and the distance fraction measures the distance it moves. These values are multiplied to give the layout shift score for each unexpected layout shift, which are then summed up over the entire lifetime of the page to provide the CLS score.

Tips to Improve Your CLS Score

1. **Specify size attributes for media:** Always include width and height size attributes on your images and videos. This helps the browser allocate the correct amount of space while the media is loading, preventing shifts.

2. **Reserve space for ad elements:** If your site uses ads, ensure that you statically reserve space for them. This prevents the content from shifting when ads are dynamically loaded.

3. **Avoid inserting new content above existing content:** Particularly after the site starts to load, unless it’s in response to a user action. This practice can significantly reduce shifts that lead to a poor user experience.

4. **Use CSS aspect ratio boxes:** For elements that need to maintain a certain aspect ratio, CSS aspect ratio property can be a lifesaver. This is particularly useful for responsive designs that need to handle different screen sizes.

5. **Preload important resources:** To avoid FOIT (Flash of Invisible Text) or FOUT (Flash of Unstyled Text), preload fonts. This ensures text remains stable as the fonts load.

6. **Optimize and test your animations:** Ensure that any CSS or JavaScript that triggers animations does so in a way that doesn’t cause layout shifts. This can often mean using transform properties instead of changing the physical dimensions or positions of elements.


Improving your CLS score is not just about boosting SEO rankings; it’s about committing to a superior user experience. At Livewire, we prioritize these metrics in our web design process, ensuring that the websites we create not only look good but are also stable, fast, and user-friendly. By focusing on these aspects, businesses can not only climb higher in search engine rankings but also retain visitors, reduce bounce rates, and ultimately convert more leads.

Whether you are building a new website or optimizing an existing one, paying attention to Cumulative Layout Shift and other Core Web Vitals is essential for success in today’s digital landscape.

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