Skip to main content

How to Measure Core Web Vitals: A Complete Guide for Web Developers

Core Web Vitals are a set of metrics that Google introduced to evaluate the user experience on websites.

These metrics measure key aspects of web performance, specifically related to loading, interactivity, and visual stability. Understanding and improving Core Web Vitals is crucial for enhancing user experience and optimising SEO, as Google uses them as part of its ranking criteria.

The Three Core Web Vitals

The three primary metrics that make up Core Web Vitals are:

  1. Largest Contentful Paint (LCP): Measures loading performance. It tracks how long it takes for the largest piece of content (typically an image or block-level element) to render in the viewport.

    • Target: LCP should occur within 2.5 seconds of when the page starts loading.

  2. First Input Delay (FID): Measures interactivity. It gauges the delay between when a user first interacts with the page (e.g., clicks a button) and when the browser begins processing that interaction.

    • Target: FID should be less than 100 milliseconds.

  3. Cumulative Layout Shift (CLS): Measures visual stability. It captures the frequency of unexpected layout shifts during a page’s lifecycle, which can cause poor user experiences.

    • Target: CLS should be less than 0.1.

Methods to Measure Core Web Vitals

There are multiple tools and approaches to measure and monitor Core Web Vitals, each suited to different purposes—from testing in a development environment to tracking real-world user experiences.

1. Google Lighthouse

Google Lighthouse is an automated tool that provides detailed insights into web page performance, including Core Web Vitals.

  • How to use: You can run Lighthouse directly from Chrome DevTools by opening a web page, right-clicking, and selecting “Inspect”. From the DevTools panel, go to the "Lighthouse" tab and run the test. Lighthouse will return a score for your site, including measurements of LCP, FID, and CLS.
  • Strengths: Lighthouse provides suggestions for optimising web performance and is easy to use for developers. It runs tests in a controlled lab environment.
  • Limitations: It doesn’t reflect real user conditions as it runs in a simulated environment.

2. PageSpeed Insights

Google's PageSpeed Insights is another powerful tool that integrates both lab data from Lighthouse and real-world data from the Chrome User Experience Report (CrUX).

  • How to use: Enter your website URL into PageSpeed Insights and click “Analyse”. The tool provides scores for both mobile and desktop, along with Core Web Vitals metrics and recommendations for improvement.
  • Strengths: Offers a combination of lab data (via Lighthouse) and field data (via CrUX), giving a broader picture of how users experience your site.
  • Limitations: Real-user data might not be available for all pages, especially those with low traffic.

3. Search Console (Core Web Vitals Report)

Google Search Console provides a dedicated report for Core Web Vitals based on real user metrics collected through the CrUX dataset.

  • How to use: In Google Search Console, navigate to the "Core Web Vitals" section under "Enhancements". This report highlights URLs that need improvement based on their LCP, FID, and CLS scores.
  • Strengths: Useful for tracking the performance of multiple pages and URLs on your website. Provides data gathered from real users.
  • Limitations: The report only flags issues and does not give granular detail on the specific causes or solutions for poor scores.

4. Chrome DevTools

Chrome DevTools offers built-in features for performance testing, including measuring Core Web Vitals in real-time during page loads.

  • How to use: Open the "Performance" tab in Chrome DevTools and start recording while interacting with the page. DevTools will show detailed results, including LCP and layout shifts during the page load.
  • Strengths: Allows developers to debug specific performance issues in real time.
  • Limitations: Requires manual interaction and is more technical, making it less user-friendly for non-developers.

5. Web Vitals Chrome Extension

The Web Vitals Chrome Extension provides a quick way to monitor Core Web Vitals as you browse the web, giving real-time measurements for LCP, FID, and CLS.

  • How to use: Install the Web Vitals Chrome Extension from the Chrome Web Store. Once installed, it shows the Core Web Vitals metrics for any page you visit.
  • Strengths: Easy to use and provides immediate feedback on any site without needing to open DevTools or other tools.
  • Limitations: Less comprehensive compared to other tools like Lighthouse or Search Console.

6. Real User Monitoring (RUM) Tools

For large websites, Real User Monitoring (RUM) is an effective method to gather real-world performance data across all visitors. Many RUM tools can be configured to track Core Web Vitals specifically.

  • Popular RUM tools:
    • Google Analytics: Custom metrics can be set up in Google Analytics to track Core Web Vitals.
    • New Relic: A performance monitoring tool that can track real-user metrics, including Core Web Vitals.
    • Dynatrace: Provides detailed performance monitoring and can be configured to collect Core Web Vitals data.
  • Strengths: Reflects actual user experience across a wide range of devices, networks, and geographic locations.
  • Limitations: Requires more complex setup and can be overwhelming for smaller websites or developers without access to such tools.

Tips for Improving Core Web Vitals

  1. Optimise Images and Media: Use modern image formats (e.g., WebP), lazy loading, and optimised image sizes to improve LCP.
  2. Reduce JavaScript Execution Time: Optimising or deferring non-critical JavaScript can lower FID.
  3. Optimise Fonts: Minimise font blocking and ensure fonts load quickly to avoid layout shifts, which improves CLS.
  4. Use a Content Delivery Network (CDN): A CDN can reduce load times by serving content from servers closer to users.
  5. Minimise Main Thread Work: Keeping the main thread free of heavy tasks can reduce input delay and improve user interaction times.
  6. Implement Best Practices for Lazy Loading: Proper lazy loading can prevent images or ads from shifting content abruptly.

The importance of measuring Core Web Vitals

Measuring Core Web Vitals is essential for improving website performance and enhancing user experience. Tools like Lighthouse, PageSpeed Insights, and Chrome DevTools offer various ways to assess these metrics, whether you are in development or monitoring real-world traffic. Continuous optimisation of LCP, FID, and CLS ensures a better experience for users and helps your website rank better in search engine results.

By leveraging these tools and addressing performance bottlenecks, web developers and SEO specialists can effectively improve their site’s Core Web Vitals, ultimately leading to more satisfied users and higher search rankings.

Related to this article are the following:

At SoftForge, we are passionate about delivering top-notch web hosting and development services that empower businesses to thrive online. Since our inception, we have been committed to innovation, quality, and customer satisfaction. Our journey is defined by our continuous pursuit of excellence and our desire to stay at the forefront of the digital industry.

From the initial concept to the final execution, we work closely with you to ensure that every aspect of your online presence is tailored to reflect your brand's identity, resonate with your target market, and support your long-term objectives. Together, we can build a digital platform that not only meets but exceeds expectations, turning your vision into a successful reality that drives growth and innovation.

Feel free to use the links below to reach out, discuss your needs, or to schedule a Google meeting with Stacey or Phil.

Contact SoftForge
Book a meeting with Phil
Book a meeting with Stacey