What is Largest Contentful Paint?
Also known as: LCP
Largest Contentful Paint (LCP) measures the time from page load until the largest visible element in the viewport is fully rendered, and is one of Google's three Core Web Vitals.
Largest Contentful Paint (LCP) is a user-centric performance metric that reports the render time of the largest image, text block, or video element visible within the initial viewport. It was introduced by Google in 2020 as part of the Core Web Vitals initiative to quantify perceived load speed. LCP replaces older metrics like load time and DOMContentLoaded because those do not reflect what the user actually sees.
LCP is calculated by the browser's PerformanceObserver API, which watches for all contentful paint events (text nodes, images, background images, and video posters) and records the render timestamp of the largest one. The metric stops reporting once the user interacts with the page (click, scroll, or keypress) or after the page has been fully loaded. A good LCP score is 2.5 seconds or faster; anything above 4.0 seconds is considered poor. Common causes of slow LCP include slow server response times, render-blocking JavaScript and CSS, slow resource load times, and client-side rendering delays.
In the performance optimization stack, LCP sits alongside First Input Delay (FID) and Cumulative Layout Shift (CLS) as one of the three Core Web Vitals. It is a key factor in Google's search ranking signals for mobile and desktop. Improving LCP typically involves optimizing the critical rendering path: preloading hero images, using a CDN, enabling compression, eliminating render-blocking resources, and implementing server-side rendering for JavaScript-heavy sites.
Key facts
- LCP is one of Google's three Core Web Vitals, alongside FID and CLS.
- A good LCP score is 2.5 seconds or less; poor is over 4.0 seconds.
- LCP measures only above-the-fold content, not the entire page.
- The metric stops recording after the first user interaction.
- Slow server response time and render-blocking resources are the most common causes of poor LCP.
How it works in practice
Related terms
References
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