Largest Contentful Paint (LCP): How to Measure and Optimise It

Imagine a user lands on a website and suddenly bounces back to the home page. Can you think of a reason why this happens? It could be low content quality, irrelevant information, or something else. But mostly, it's the slow loading of the Largest Contentful Paint (LCP). What is LCP? It is a web performance metric that measures how quickly the largest elements, such as images, videos, and text, display on the site.

In this blog, we’ll delve into the Largest Contentful Paint, how you can measure the LCP of your site and strategies to boost your website’s LCP score.

Table of Contents

1) What is Largest Contentful Paint (LCP)?

2) What's a Good LCP Score?

3) How to Measure Largest Contentful Paint (LCP)?

4) Strategies to Optimise Largest Contentful Paint (LCP)

5) Factors Affecting LCP and Causes of a Slow Score

6) Conclusion

What is Largest Contentful Paint (LCP)?

The Largest Contentful Paint (LCP) is a Core Web Vital that estimates the time it takes for the largest segment of your site to become visible in the viewport. Until LCP is completed, you’ll see very little on the page, as this segment is usually located above the fold — the top part.

LCPs typically consist of images or text blocks, but they can also be videos or animations. The segment might vary between mobile and desktop views.

The largest segment impacts User Experience and perceived load speed, so it must load quickly. A delay or wait can leave users staring at a page with no text or image, potentially causing them to leave the site. A few seconds of delay can seriously affect user behaviour.

Google introduced LCP in its Core Web Vitals, which are metrics that gauge User Experience. LCP will contribute to new ranking factors like the Page Experience Signal, making it essential for improving User Experience and boosting Search Engine Optimisation.

Additionally, LCP accounts for 25% of the total PageSpeed Insights score. Improving it will likely increase your page speed rating.

What's a Good LCP Score?

A good Largest Contentful Paint (LCP) score primarily impacts User Experience. Typically, LCP should be 2.5 seconds or less. Scores within this range imply that users can view the most important content on your page quickly, improving their browsing experience.

LCP scores between 2.5 and 4 seconds require improvement, which may result in user frustration and higher bounce rates. An LCP score beyond 4 seconds is considered poor, signalling a slow-loading page that can greatly deter users from engaging further with your content.

To attain a good LCP score, focus on optimising images, minimising server response times, and utilising efficient loading strategies.

How to Measure Largest Contentful Paint (LCP)?

You can measure LCP using several tools and methods. Let’s explore some popular tools:

a) Google PageSpeed Insights: This tool analyses your webpage's performance, including LCP scores. To check your LCP score, first, enter your URL in the box available, and you'll be presented a report highlighting your site's LCP metrics.

b) Web Vitals Extension: This Chrome extension shows the Largest Contentful Paint (LCP) metrics in real-time while you browse. It provides insights into how quickly an element on your website loads as you navigate it.

c) Lighthouse: Built into Chrome DevTools, Lighthouse is a robust tool for evaluating web performance. Open DevTools, select the "Lighthouse" tab and perform an audit to get an outline of your LCP and other Core Web Vitals.

d) Real User Monitoring (RUM): RUM tools like Google Analytics or other monitoring solutions are used to check LCP for active site users in real-time.

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Strategies to Optimise Largest Contentful Paint (LCP)

Improving LCP can bring positive results like high user engagement, improved search ranking, etc. Here are some strategies to optimise LCP:

1) Optimise Image Sizes

Improving image sizes is a highly effective method for boosting your website's LCP. Make sure that images are not bigger than needed for the space they are shown in. Use suitable formats like WebP or AVIF, which offer excellent quality with reduced file sizes.

Moreover, it is recommended to use responsive images with the 'srcset' attribute to provide various image sizes depending on the device's screen resolution. This ensures that smaller images are sent to mobile users, enhancing loading speeds.

2) Utilise an Image CDN

Utilising an Image Content Delivery Network (CDN) can significantly improve LCP. An image CDN stores elements like images and videos on servers closer to your users, reducing latency and load times.

CDNs also provide automatic image optimisation features, resizing images according to user device and internet connection. Faster image delivery enhances LCP and smoothens the User Experience.

3) Avoid Loading Images With JavaScript

Loading images via JavaScript can delay the display, negatively impacting LCP. Instead, use HTML tags for critical images to ensure the browser prioritises them during the initial loading phase.

Use the loading="lazy" attribute for lazy loading non-essential images but be mindful to prioritise the loading of the largest contentful element. This prevents delays in its visibility.

4) Select a Reliable Hosting Service

A good LCP score largely depends on the performance of your web hosting service. Pick a reliable hosting service provider with faster server response times and uptime. Avoid shared hosting plans as it may result in slower performance due to resource contention. You can even go for dedicated or VPS hosting for high speed and reliability.

Furthermore, ensure that your hosting service offers HTTP/2, which can enhance loading efficiency by permitting multiple requests to be sent simultaneously.

By applying these strategies, you can improve your LCP score. Don’t forget to monitor your performance metric to stay competitive in search rankings.

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Factors Affecting LCP and Causes of a Slow Score

For a site, three factors affect LCP: Render-blocking JavaScript, slow resource load time, and slow server response time. Let’s explore each in detail and how to fix it:

1) Slow Server Response Time

Delays in server response can significantly impact content loading speed when a browser requests from the server. When the server is slow to transfer data, it hinders the browser's ability to display content promptly, resulting in lagging load times and a decrease in the LCP score.

To tackle this issue, enhance your Time to First Byte (TTFB), utilise a Content Delivery Network (CDN), and create early links to third-party services.

2) Render-blocking JavaScript and CSS

After receiving data from the server, the browser needs to analyse the HTML to develop a Document Object Model (DOM) tree to display the content. This process may be postponed if JavaScript or CSS files block rendering. It delays browsers' HTML processing, leading to increased loading times and a decreased LCP score.

To address this issue, consider delaying or deleting JavaScript files that are not being used, as this can significantly improve the page's load time.

3) Slow Resource Load Times

Additional elements like photos, videos, and block-level elements such as HTML and CSS files can also negatively impact performance. Because LCP focuses on the elements at the top of the page, a delay in loading these resources can cause a delay in rendering, especially if they are placed above the fold. Optimise images and compress CSS, JavaScript, and HTML files to enhance resource load times.

Conclusion

Largest Contentful Paint (LCP) is the most vital metric for evaluating User Experience on a website. Prioritising improving load times for the most significant visible elements can significantly increase user satisfaction and interaction. One should focus on techniques like optimising images, improving server response, and reducing render-blocking resources to enhance the LCP score.

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