Core Web Vitals – What and Why to Improve for Ranking

The term “Core Web Vitals” refers to a group of metrics introduced by Google to measure a webpage’s speed, responsiveness, and visual stability. These factors are crucial in determining the overall user experience on a website. The Core Web Vitals consist of three specific metrics: Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS).

These metrics are not just fancy technical terms; they play a significant role in Search Engine Optimization (SEO) and page ranking. Google has made it clear that a website’s performance, as measured by these vitals, will impact its search rankings. Therefore, understanding and optimizing Core Web Vitals is essential for anyone looking to improve their website’s visibility and ranking on Google’s search engine results pages (SERPs).

What are Core Web Vitals?

Core Web Vitals are a set of metrics developed by Google that measure the quality of user experience on a website. These metrics focus on three main aspects of user experience: loading, interactivity, and visual stability. The three metrics that measure these aspects are LCP, FID, and CLS.

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  • Largest Contentful Paint (LCP): measures the loading performance of a website. It tracks the time it takes for the largest content element on the page to load. A good LCP score is less than 2.5 seconds.
  • First Input Delay (FID): measures the interactivity of a website. It tracks the time it takes for a user to interact with a website after the first click. A good FID score is less than 100 milliseconds.
  • Cumulative Layout Shift (CLS): measures the visual stability of a website. It tracks how much the layout of a page shifts as it loads. A good CLS score is less than 0.1.

Google considers Core Web Vitals as a crucial set of performance metrics for all web pages, and all site owners should measure and optimize them. They are designed to measure how a real-world user would perceive the experience of a webpage, beyond just the raw technical parameters. The vitals focus on three aspects of user experience: loading, interactivity, and visual stability, and they include three specific metrics: Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS). Let’s delve into each of these metrics in detail.

Largest Contentful Paint (LCP)

Largest Contentful Paint (LCP) is a performance metric that measures how long it takes for the largest content element on a webpage to become visible within the viewport. This could be an image, a video, or even a text block. The “largest” element is typically the one that takes up the most space on the viewport.

LCP is a crucial metric because it clearly indicates when the main content of a page has finished rendering on the screen. This is important because users can’t interact with a webpage until the main content has loaded. If the LCP is too high, users may perceive the page as slow, leading to a poor user experience.

Google suggests that to provide a good user experience, LCP should occur within 2.5 seconds of when the page first starts loading. To improve LCP, you can consider strategies such as optimizing server response times, enabling caching, compressing images, and minifying CSS. Removing any render-blocking JavaScript and CSS that could interfere with loading the largest contentful paint is also crucial.

First Input Delay (FID)

First Input Delay (FID) is a user-centric metric for measuring load responsiveness. It quantifies the experience users feel when trying to interact with unresponsive pages — a low FID helps ensure that the page is usable.

FID measures the time from when a user first interacts with your page (when they click a link, tap on a button, etc.) to when the browser can actually respond to that interaction. This delay is usually caused by the browser being busy with other tasks, such as loading heavy JavaScript files.

A low FID is a sign of a website that is interactive and responsive to user inputs. Google recommends an FID of less than 100 milliseconds for a good user experience. To improve FID, minimize (or defer) JavaScript, use a web worker, and keep request counts low and transfer sizes small. Breaking up Long Tasks can also help reduce FID, as well as other interactivity metrics.

Cumulative Layout Shift (CLS)

Cumulative Layout Shift (CLS) is a metric that measures visual stability. It quantifies how many elements on the page shift during loading. This is important because the unexpected movement of page content usually results in a poor user experience.

The CLS score is calculated by looking at the impact and distance fractions. The impact fraction measures how much an unstable element impacts the viewport area between two frames. The distance fraction measures the distance that unstable elements have moved relative to the viewport.

A low CLS score means the page is stable; a high CLS score means elements on the page shift around a lot during load, which can be frustrating for users. Google recommends a CLS score of less than 0.1 for a good user experience.

Improving CLS involves always including size attributes on your images and video elements or otherwise ensuring text doesn’t change size as web fonts load. It also involves avoiding inserting content above existing content unless in response to user interaction.

Why do Core Web Vitals matter?

Core Web Vitals are essential because they directly impact the user experience. A website that loads slowly is unresponsive or has a layout that constantly shifts is frustrating for users and can lead to a high bounce rate. Google uses Core Web Vitals as a ranking factor in search results, meaning websites that perform poorly on these metrics are less likely to be visible in search results.

Tools for Measuring Core Web Vitals

Several tools are available to measure Core Web Vitals, including Google’s own suite of tools. Google Search Console provides:

  • A dedicated report on Core Web Vitals.
  • Offering site-wide metrics for mobile and desktop.
  • Highlighting any pages that need attention.

PageSpeed Insights is another Google tool that provides information on Core Web Vitals. It offers both real-world (field) data and lab data about a page’s performance. You can use Chrome DevTools to measure Core Web Vitals, which gives you more granular, per-interaction measurements.

Other tools and APIs, such as the Chrome User Experience Report (CrUX), Lighthouse, and Web Vitals JavaScript library, can also be used to measure and report on Core Web Vitals.

Checking the Report

To check the Core Web Vitals report for your website in Google Search Console, follow these steps:

  1. Sign in to your Google Search Console account.
  2. Select the website you want to check.
  3. Click on “Core Web Vitals” in the left-hand menu.
  4. Review the report to see how your website performs on the three metrics.

Crux Data

The Core Web Vitals report in Google Search Console also includes CrUX (Chrome User Experience) data. This data is collected from real user experiences and provides additional insights into how users interact with your website. It includes metrics like TTFB (Time to First Byte), FCP (First Contentful Paint), TBT (Total Blocking Time), and TTI (Time to Interactive).

  • Time to First Byte (TTFB): measures the time it takes for the first byte of data to be received from the server. A good TTFB score is less than 200 milliseconds.
  • First Contentful Paint (FCP): measures the time it takes for the first piece of content to be rendered on the screen. A good FCP score is less than 1.5 seconds.
  • Total Blocking Time(TBT): measures the time it takes for a page to become interactive. A good TBT score is less than 300 milliseconds.
  • Time to Interactive (TTI): measures the time it takes for a webpage to become fully interactive, allowing users to interact with all the elements on the page. A good TTI score is less than 5 seconds.

Measuring these metrics can help identify specific issues with a web page’s performance and provide insights into how to improve them.

The Impact of Core Web Vitals on SEO

Core Web Vitals are a part of Google’s Page Experience signals, which are a set of factors that Google uses to measure how users perceive the experience of interacting with a web page beyond its pure information value. It includes

  • Core Web Vitals,
  • mobile-friendliness,
  • safe browsing,
  • HTTPS security,
  • and intrusive interstitial guidelines.

Google has stated that these signals will be included in its search rankings. This means that websites providing a poor user experience as per these metrics, may rank lower in search results, while those providing a good experience may receive a boost and rank higher.

Several case studies and real-world examples have shown the impact of Core Web Vitals on SEO. For instance, websites that improved their Core Web Vitals saw a significant increase in organic traffic and improved SERP rankings. Therefore, optimizing for these vitals is not just about improving user experience but also about enhancing the website’s visibility and ranking on Google.

Future of Core Web Vitals

Google has indicated that the set of metrics in Core Web Vitals will evolve over time based on user expectations and changing trends in web design. The company has also stated that the thresholds for the existing metrics may be updated or new metrics may be added to better capture user experience.

For instance, Google has announced that it will replace FID with a new metric called First Input Timing (FIT) in the future. This shows that Google is committed to refining these metrics to ensure they accurately measure the aspects of user experience that matter most.

The role of Core Web Vitals in SEO practices is also expected to evolve. As these metrics become more ingrained in SEO strategies, businesses and web developers will need to continuously monitor and optimize these vitals to ensure their websites remain competitive in search rankings.


In conclusion, Core Web Vitals are a crucial aspect of user experience and SEO. They provide measurable indicators of website performance and user engagement, which directly impact a site’s ranking on Google.

While optimizing for these vitals can be technical and complex, the benefits in terms of improved user experience and enhanced SEO are significant. With the future of web revolving around user experience, understanding and optimizing for Core Web Vitals will be key to a successful and competitive website.

As Google continues to refine these metrics and incorporate them into its ranking algorithms, staying updated with the latest developments in Core Web Vitals will be crucial for SEO professionals, web developers, and website owners.

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