Core Web Vitals explained in plain English.

What are Core Web Vitals?

Core Web Vitals are three metrics Google uses to measure real-world user experience on a web page: how quickly the main content loads, how quickly the page responds when someone interacts with it, and how stable the layout is while it loads. They are part of Google's page experience signals.

• LCP (Largest Contentful Paint) measures loading.
• INP (Interaction to Next Paint) measures responsiveness.
• CLS (Cumulative Layout Shift) measures visual stability.

What are good Core Web Vitals scores?

Google rates each metric as good, needs improvement or poor. To pass, at least 75% of real visits to a page should fall in the good range:

• LCP: 2.5 seconds or less is good; over 4 seconds is poor.
• INP: 200 milliseconds or less is good; over 500 milliseconds is poor.
• CLS: 0.1 or less is good; over 0.25 is poor.

What is LCP and how do I improve it?

Largest Contentful Paint is the time it takes for the biggest visible element, usually a hero image, video poster or large heading, to appear on screen. A slow LCP makes a page feel like it isn't loading.

• Compress and resize the hero image, and serve it as WebP or AVIF.
• Don't lazy-load the LCP image. Load it eagerly and consider fetchpriority="high".
• Reduce server response time (TTFB) with caching or a CDN.
• Remove render-blocking CSS and JavaScript from the top of the page.

What is INP and how do I improve it?

Interaction to Next Paint measures the delay between a visitor clicking, tapping or typing and the page visibly responding. It replaced First Input Delay (FID) as a Core Web Vital in March 2024. Poor INP is almost always caused by too much JavaScript running on the main thread.

• Remove unused scripts, plugins and third-party tags.
• Break long JavaScript tasks into smaller chunks.
• Delay non-essential scripts such as chat widgets until after the page loads.
• Avoid heavy work inside click and input handlers.

What is CLS and how do I improve it?

Cumulative Layout Shift measures how much content jumps around while the page loads. It's the reason you sometimes tap the wrong button because an ad pushed it down.

• Always set width and height (or aspect-ratio) on images and videos.
• Reserve space for ads, embeds and banners before they load.
• Use font-display: swap with a closely matched fallback font.
• Don't insert content above existing content unless the user asked for it.

Do Core Web Vitals affect SEO rankings?

Yes, but modestly. Google has confirmed Core Web Vitals are a ranking signal, and relevance still matters far more. Where they make a bigger difference is conversions: faster, more stable pages keep more visitors and sell more. Think of them as a tiebreaker for rankings and a multiplier for revenue.

Lab data vs field data

Tools such as Lighthouse produce lab data: a simulated load on a set device and network. Google's rankings use field data from real Chrome users (the Chrome UX Report). Lab scores are great for diagnosing problems; field data tells you what visitors actually experience. Small or new sites often don't have enough traffic for field data, so lab data is the best guide.

Want the full list of speed problems, not just the scores? Read why your website is slow, or run a free speed test on your own site.

Frequently asked questions

Written by Sudharma at Pagelyt.