Core Web Vitals Explained: LCP, INP and CLS

Core Web Vitals are a set of metrics from Google that measure how real people experience the speed and stability of your web pages. They are part of Google’s page experience signals, and more importantly, they reflect whether your site feels fast and pleasant to use. Here is what each metric means and how to improve it.

The three Core Web Vitals

Largest Contentful Paint (LCP) — loading

LCP measures how long it takes for the largest visible element — often a hero image or main heading — to appear. A good LCP is 2.5 seconds or less.

Interaction to Next Paint (INP) — responsiveness

INP measures how quickly the page responds visually after a user interacts, such as clicking a button or opening a menu. It replaced First Input Delay (FID) as a Core Web Vital in March 2024. A good INP is 200 milliseconds or less.

Cumulative Layout Shift (CLS) — visual stability

CLS measures how much content unexpectedly moves around while the page loads — for example, text jumping down when an image or ad appears. A good CLS is 0.1 or less.

Google assesses these at the 75th percentile of real page loads, so most of your visitors need a good experience for a page to pass.

Where to find your scores

• PageSpeed Insights shows both field data from real Chrome users (when available) and lab data from a simulated test.
• Google Search Console groups your URLs into good, needs improvement and poor.
• Chrome DevTools (Lighthouse and the Performance panel) helps diagnose specific problems.

How to improve LCP

• Optimise the hero image: serve it in WebP or AVIF, at the right size, and don’t lazy-load it. Consider fetchpriority="high".
• Reduce server response time with good hosting and page caching.
• Remove render-blocking resources: defer non-critical JavaScript and keep CSS lean.
• Use a CDN to deliver files from servers close to your visitors.
• Load fonts efficiently with font-display: swap and as few font files as possible.

How to improve INP

• Reduce JavaScript. Every script competes for the browser’s main thread. Remove what you don’t need.
• Break up long tasks so the browser can respond to input between them.
• Be careful with third-party scripts such as chat widgets, heatmaps and tag managers; load them later or only where needed.
• Avoid heavy page builders that generate large amounts of script and markup.

How to improve CLS

• Always set width and height (or an aspect ratio) on images and videos.
• Reserve space for ads and embeds so they don’t push content down when they load.
• Avoid inserting content above existing content, such as banners that appear after load.
• Prefer transform-based animations over animating properties that change layout.

Performance on WordPress

On WordPress, the biggest improvements usually come from a lightweight theme, fewer plugins, image optimisation, a caching plugin (for example LiteSpeed Cache on LiteSpeed hosting) and a CDN. Measure before and after each change so you know what helped.

Why it matters beyond SEO

Faster, more stable pages lead to lower bounce rates and higher conversions. Visitors are more likely to read, trust and act on a site that responds instantly. Treat Core Web Vitals as a user experience goal, and the search benefits follow.