Is Cumulative Layout Shift dragging your website down?

Have you ever gone to click a button on a website only for it to shift, causing you to miss, or worse, clicking the wrong thing?

This issue, known as cumulative layout shift, disrupts user experience and impacts page speed and search engine optimisation. For small- and medium-sized business owners, understanding the effects of cumulative layout shift is crucial for maintaining a competitive online presence. A poor cumulative layout shift score can slow down page speed, frustrate users, and harm your search engine optimisation efforts, ultimately lowering your site's ranking on Google. In this article, we’ll explain what cumulative layout shift is, how it affects page speed and SEO, and how to identify and fix it using online tools.

What Is Cumulative Layout Shift?

Defining Cumulative Layout Shift

Cumulative layout shift (CLS) is a Core Web Vitals metric that measures visual stability on a webpage. It quantifies how much content, like images or text, moves unexpectedly as the page loads. CLS is calculated by multiplying the impact fraction (the portion of the viewport affected) by the distance fraction (how far elements shift). A low CLS score, ideally below 0.1, indicates a stable page, while scores above 0.25 suggest poor stability, as noted in understanding cumulative shift. These shifts frustrate users, impacting their experience and your site’s performance.

Why CLS Matters for Businesses

Unexpected layout shifts can lead to user frustration, increasing bounce rates and reducing engagement. For businesses, this means fewer conversions and lower revenue. CLS also ties directly to page speed, as unstable layouts slow down the perceived loading time, affecting user satisfaction and SEO rankings.

Impact of CLS on Page Speed

How CLS Slows Down Perceived Page Speed

While cumulative layout shift doesn’t directly impact server-side loading times, it affects how users perceive page speed. When elements shift during loading, users must wait longer to interact with the page, making it feel sluggish. For example, a button moving due to a late-loading ad delays user actions, effectively reducing page speed. This poor experience can lead to higher abandonment rates, especially on mobile devices where fast page speed is critical.

CLS and Device Performance

Mobile users, who often rely on slower connections, are particularly sensitive to CLS issues. A high CLS score exacerbates delays in page rendering, further harming perceived page speed. Optimising CLS ensures a smoother experience across devices, improving user retention and engagement.

CLS and Search Engine Optimisation

CLS as a Ranking Signal

Google’s Core Web Vitals, including CLS, are integral to search engine optimisation. A high CLS score signals poor user experience, which can lower your site’s ranking in search results. Since Google prioritises fast, stable websites, optimising CLS is essential for maintaining visibility and driving organic traffic.

Indirect SEO Impacts

Beyond direct ranking effects, CLS influences user behaviour metrics like bounce rate and dwell time, which indirectly affect SEO. If layout shifts frustrate users, they’re more likely to leave quickly, signalling to Google that your content may not be valuable. Improving CLS enhances user engagement, boosting search engine optimisation outcomes.

Identifying CLS with Online Tools

Using Lighthouse to Measure CLS

Google’s Lighthouse is a powerful tool for identifying CLS issues. By running an audit with Lighthouse, you can pinpoint elements causing layout shifts and receive recommendations for fixes. PageSpeed Insights also provides CLS scores, helping you assess your site’s performance against Google’s benchmarks.

Other Tools for CLS Analysis

Additional tools like WebPageTest and Chrome DevTools can help diagnose CLS. WebPageTest offers detailed reports on layout shifts, while Chrome DevTools’ Performance panel visualises shifts in real-time. Regularly auditing your site ensures you catch CLS issues early, maintaining optimal page speed and SEO.

How to Fix Cumulative Layout Shift

Addressing Common CLS Causes

Several factors contribute to CLS, but they can be fixed with targeted strategies:

• Images and ads: Specify width and height attributes for images and reserve space for ads to prevent shifts.
• Web fonts: Use font-display: swap or preload critical fonts to avoid text movement.
• Dynamic content: Minimise late-loading elements like pop-ups that disrupt layout.
• Third-party scripts: Defer or optimise scripts to reduce unexpected content injections.

Practical Steps for Improvement

To reduce CLS, start with a Lighthouse audit to identify problem areas. Then, implement fixes like setting image dimensions and optimising fonts. Regularly test your site to ensure CLS stays below 0.1, improving both page speed and user experience.

Why Choose Status 218?

At Status 218, we specialise in optimising websites for CLS, page speed, and search engine optimisation. Our team provides tailored solutions to enhance your site’s performance, ensuring a seamless user experience and better rankings.

Conclusion

We later explored the real-world business cost of layout shift in Why Your Website Buttons Keep Moving and What It's Costing You.

CLS is one component of the broader page speed picture — we covered the importance of page speed in How Important Is Page Speed for Search Engine Rankings?