What is Cumulative Layout Shift (CLS) and How to Optimize CLS?

What is Cumulative Layout Shift (CLS) and How to Optimize CLS?

The ever-evolving landscape of SEO has witnessed the rise of new metrics that go beyond traditional SEO factors such as keywords and backlinks. Google’s Core Web Vitals, a set of user-centric measurements, play a pivotal role in assessing the overall user experience offered by websites. Among these metrics, CLS has emerged as a significant ranking factor, directly influencing your website’s visibility in search engine results.

In this article, we will dive deep into the significance of CLS and explore practical strategies for improving this vital metric within your website. Whether you’re an SEO specialist, a web developer, or a business owner seeking to enhance your website’s visibility, understanding CLS and its impact is crucial in today’s competitive digital landscape.

What is CLS (Cumulative Layout Shift)?

What is Cumulative Layout Shift (CLS) and How to Optimize CLS?

CLS stands for Cumulative Layout Shift, and it is a user-centric metric that measures the visual stability of web pages as they load. In the context of SEO (Search Engine Optimization), CLS plays a crucial role in determining a website’s search engine rankings.

CLS takes into account the unexpected shifting of visual elements on a webpage during the loading process. Elements such as images, ads, or other resources that load slowly or cause delays can result in a poor user experience if they cause the content layout to shift suddenly. This can lead to frustration and annoyance for users, negatively impacting their overall satisfaction with the website.

In terms of SEO, a low CLS score is desirable, indicating that the content on a webpage remains visually stable during loading. Websites with low CLS scores are more likely to be ranked higher in search engine results, as they offer a better user experience.

Importance of CLS

CLS is an important metric in the field of SEO (Search Engine Optimization). It is a user-centric performance metric that measures visual stability on web pages. In simple terms, CLS gauges how much the content on a web page shifts around as it loads, affecting the user experience. A good CLS score means that the page loads smoothly without unexpected layout shifts, while a poor score indicates a jumpy and disruptive experience for users.

Here are some reasons why CLS is important for SEO:

  • User Experience (UX): Search engines, especially Google, prioritize user experience when ranking web pages. Websites that provide a smooth and pleasant browsing experience are more likely to rank higher in search results.
  • SEO Rankings: As mentioned earlier, search engines consider user experience as a ranking factor. Google has been increasingly incorporating Core Web Vitals (of which CLS is one) into its ranking algorithms. Websites with better CLS scores are likely to be rewarded with higher rankings, leading to increased organic traffic.
  • Mobile Friendliness: Mobile devices account for a significant portion of web traffic. On mobile devices, CLS can have a more significant impact due to varying network conditions and smaller screens. Websites with good CLS scores are more likely to perform well on mobile devices, enhancing their overall mobile-friendliness.
  • Reduced Bounce Rates: A positive user experience, driven in part by a low CLS, can reduce bounce rates. When users encounter a page that is visually stable and loads quickly, they are more likely to stay and explore the content, reducing the chances of them bouncing back to the search results.
  • User Engagement: Improved user experience often leads to increased user engagement metrics, such as longer time spent on the site, more pages viewed per session, and lower exit rates. These signals can further positively influence your SEO efforts.
  • Mobile-First Indexing: Google has shifted to a mobile-first indexing approach, where the mobile version of your website is primarily used for ranking and indexing. Since CLS is especially important on mobile devices, it directly impacts how your site performs in mobile-first indexing.

How CLS Score is Measured?

How CLS Score is Measured

Cumulative Layout Shift (CLS) is measured using a metric that calculates the sum total of all individual layout shifts that occur within a web page during its load time. Each layout shift is assigned a score based on the distance the element moves and its impact on the viewport. The CLS score is the sum of these individual scores, reflecting the overall amount of unexpected shifting that users experience.

Google’s PageSpeed Insights and Lighthouse are commonly used tools to measure CLS, providing a numerical value that indicates the extent of layout shifts on a scale from 0 to 1. A lower CLS score signifies a more stable and user-friendly website, while higher scores indicate the need for improvement to minimize unexpected layout movements.

A Good CLS Score?

A good Cumulative Layout Shift (CLS) score is typically considered to be less than 0.1. This score indicates minimal visual instability and a smooth user experience during the loading and rendering of a webpage.

A lower CLS score indicates that the layout of the page remains stable, with no or minimal shifts in content, reducing user frustration and providing a positive browsing experience. Google considers a CLS score of 0.1 or lower as a threshold for a good user experience and encourages website owners to strive for that benchmark.

However, it’s important to note that as with other performance metrics, the lower the CLS score, the better. Striving for a CLS score as close to zero as possible ensures an optimal user experience, improves search engine rankings, and helps retain visitors to your website.

How to Optimize CLS?

Optimizing Cumulative Layout Shift (CLS) involves implementing various strategies to minimize unexpected layout shifts during webpage loading.

  • First, avoid inserting content dynamically or making changes to element sizes after the initial page load, as these actions can cause shifts. Setting explicit dimensions for images, videos, and other media elements helps maintain stability.
  • Preloading and reconnecting assets, such as images, fonts, and CSS files, ensures they are ready before they are needed. Lazy loading can be employed for media elements to defer their loading until they enter the viewport.
  • Optimal use of web fonts, including font/display swaps and fallback fonts, reduces layout shifts caused by font loading. Reserving space for ads with fixed aspect ratios prevents sudden shifts when ads appear.
  •  Minimizing the usage of third-party scripts or lazy loading them can also mitigate layout shifts.
  • Finally, regularly testing and monitoring CLS scores using tools like Google PageSpeed Insights or Lighthouse enables ongoing optimization for a smoother user experience.

How Cumulative Layout Shift Score Impact on SEO?

how to optimize cls

The Cumulative Layout Shift (CLS) score has a significant impact on the SEO performance of a website. CLS, which measures the visual stability of a webpage, plays a crucial role in enhancing user experience and engaging visitors.

A low CLS score indicates a smoother browsing experience, reducing frustration and increasing user satisfaction. This positive user experience leads to longer sessions, lower bounce rates, and higher engagement metrics, all of which are considered important ranking factors by search engines.

Additionally, with Google’s focus on Core Web Vitals, including CLS, websites with better CLS scores are more likely to rank higher in search engine results pages.

By optimizing CLS, website owners can improve their search engine visibility, attract more organic traffic, and gain an edge over their competitors in the highly competitive world of SEO.


In this blog, we have explored the crucial role of Cumulative Layout Shift (CLS) in driving SEO success. We’ve learned that CLS is a vital metric within Google’s Core Web Vitals, measuring the visual stability of web pages as they load. A high CLS score can lead to a poor user experience and lower search engine rankings, while a low score can provide a seamless and engaging user experience.

Remember, a well-optimized website is not only beneficial for search engines but also for your users. By prioritizing user experience through minimizing layout shifts, you are creating a more pleasant and engaging environment for your visitors. This will result in longer session durations, lower bounce rates, and higher user satisfaction – all factors that search engines value highly.