Core Web Vitals

Core Web Vitals: The Key Metrics for Website User Experience Optimization

This comprehensive guide will teach you how to optimize your website for Core Web Vitals, the key metrics for website user experience. By focusing on these critical metrics, you can improve your search engine rankings, user engagement, and conversion rates. Learn how to improve LCP, FID, and CLS while avoiding common pitfalls. Begin optimizing your website today for improved user experience and search engine rankings.

What are Core Web Vitals?

Core Web Vitals are a set of metrics that Google uses to measure the quality of user experience on websites. Core Web Vitals is comprised of three key metrics:

  1. Largest Contentful Paint (LCP): This measures the time it takes for the largest piece of content on a page (usually an image or video) to load and become visible to the user.
  2. First Input Delay (FID): This measures the time it takes for a user to interact with a page for the first time (e.g. clicking a button) and the time it takes for the page to respond to that interaction.
  3. Cumulative Layout Shift (CLS): This measures the amount of unexpected layout shifts that occur on a page during the loading process. An example of this would be when a user is reading an article and suddenly the page jumps due to an image or ad loading.

Why do Core Web Vitals matter?

Core Web Vitals are important because they influence how Google ranks your website in search results. In other words, if your website has low Core Web Vitals, it is less likely to rank high in search results. Furthermore, websites with high Core Web Vitals have higher user engagement and conversion rates.

How are Core Web Vitals measured?

Google’s Chrome User Experience Report collects real-world user data to calculate Core Web Vitals (CrUX). This information is then used to calculate scores for each of the three metrics. The worst-performing metric out of the three is used to calculate a website’s overall Core Web Vitals score.

Largest Contentful Paint (LCP)

The time it takes for the largest piece of content on a page to load and become visible to the user is measured by LCP. LCP scores of less than 2.5 seconds are considered good.

First Input Delay (FID)

FID is the time it takes for a user to interact with a page for the first time and for the page to respond to that interaction. FID scores of less than 100 milliseconds are considered good.

Cumulative Layout Shift (CLS)

CLS counts the number of unexpected layout shifts on a page that occur during the loading process. When a user is reading an article and the page suddenly jumps due to an image or ad loading, this is an example of this. CLS scores of less than 0.1 are considered good.

How to measure and analyze Core Web Vitals

Google offers a variety of tools for measuring and analyzing Core Web Vitals. The most commonly used tool is PageSpeed Insights, which provides a detailed report on the performance of a website, including Core Web Vitals. This tool also recommends ways to improve performance.

Another tool that provides information on Core Web Vitals is Google Search Console. The Core Web Vitals report in Search Console provides an overview of a website’s Core Web Vitals performance and identifies areas for improvement.

How to optimize your website for Core Web Vitals

Improving the performance of each of the three metrics is part of optimizing your website for Core Web Vitals. Here are some pointers to help you improve each of the three metrics:

Tips for improving LCP

  • Optimize images and videos: Reduce the file size of images and videos by compressing them without losing quality. You can use tools like Adobe Photoshop or TinyPNG to compress images.
  • Use a content delivery network (CDN): A CDN can improve the loading time of large content by delivering content from a server that is closest to the user.
  • Eliminate render-blocking resources: This includes JavaScript and CSS files that prevent the page from rendering quickly.

Tips for improving FID

  • Minimize JavaScript execution time: JavaScript can significantly impact FID, so it’s important to minimize its execution time by reducing the amount of JavaScript on your page or deferring its loading.
  • Optimize server response time: A slow server can significantly impact FID. You can improve server response time by optimizing server configurations, reducing server requests, and using caching.

Tips for improving CLS

  • Set size attributes for images and videos: By setting the size attribute, the browser can reserve the appropriate amount of space on the page for the content, preventing unexpected layout shifts.
  • Avoid inserting new content above existing content: This can cause existing content to move down the page, resulting in a layout shift.
  • Load ads and iframes with a reserved space: This ensures that there is a designated space for ads and iframes to load, preventing unexpected layout shifts.

Common mistakes to avoid

Here are some of the most common mistakes website owners make when optimizing for Core Web Vitals:

  • Focusing too much on one metric: While each metric is important, it’s important to optimize for all three to achieve a good overall Core Web Vitals score.
  • Ignoring mobile performance: With mobile devices accounting for a large portion of website traffic, it’s important to ensure that your website performs well on mobile devices.
  • Over-optimizing: Trying to optimize too much can result in a negative impact on user experience. It’s important to find a balance between optimization and user experience.


Core Web Vitals are an important factor in determining the quality of a website’s user experience. You can improve search engine rankings, user engagement, and conversion rates by optimizing your website for Core Web Vitals. Remember to pay attention to all three metrics and to use Google’s tools to measure and analyze the performance of your website.


  1. What are some other tools for measuring Core Web Vitals?
  • Other tools include WebPageTest, GTmetrix, and Lighthouse.
  1. Can poor Core Web Vitals affect ad revenue?
  • Yes, poor Core Web Vitals can result in lower ad revenue as a result of lower user engagement and pageviews.
  1. What is a good Core Web Vitals score?
  • A good Core Web Vitals score is one that meets the recommended thresholds for all three metrics: LCP under 2.5 seconds, FID under 100 milliseconds, and CLS under 0.1.
  1. How often should I measure Core Web Vitals?
  • Core Web Vitals should be measured on a regular basis, at least once a month, to ensure that your website is performing well.
  1. Is optimizing for Core Web Vitals difficult?
  • Optimizing for Core Web Vitals can be a difficult process, but it is critical for website owners to invest the time and resources necessary to optimize their website for these metrics. While some technical knowledge and expertise may be required, there are numerous resources available to assist website owners in improving the performance of their website. Optimizing for Core Web Vitals can ultimately lead to a better user experience, higher search engine rankings, and increased revenue.
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As a London-based Technical SEO Strategist, I've worked with top firms like,, Tripadvisor, Yopa, and various digital marketing and cloud computing companies. My extensive experience in SEO, including outreach, helps me create impactful strategies informed by the latest industry trends, ensuring innovative solutions for diverse industry needs.

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