Core Web Vitals: LCP, INP and CLS Explained

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Core Web Vitals: LCP, INP and CLS Explained – SEOTT guide

Core Web Vitals are three metrics Google uses to measure real-world user experience on a page: how fast the main content loads, how quickly the page responds to input and how stable the layout is. They form part of Google’s page experience signals and sit within technical SEO.

The three metrics

Largest Contentful Paint (LCP)

The time until the largest image or text block in the viewport is displayed. Good: 2.5 seconds or less. Poor: over 4 seconds.

Interaction to Next Paint (INP)

How long the page takes to respond visually after a click, tap or key press, measured across the visit. INP replaced First Input Delay in March 2024. Good: 200 milliseconds or less. Poor: over 500 ms.

Cumulative Layout Shift (CLS)

How much visible content jumps around while the page loads. Good: 0.1 or less. Poor: over 0.25.

A page passes when 75% of real visits meet the “good” threshold for all three. Google sets out each threshold in its Web Vitals guide.

Do Core Web Vitals affect rankings?

Yes, but modestly. Google has said relevance and quality come first; vitals act more like a tie-breaker. Their bigger impact is on conversions. Faster, stable pages keep visitors, and visitors who stay are more likely to buy, enquire and share.

How to check your scores

  • Search Console: the Core Web Vitals report groups URLs by template using real Chrome user data.
  • PageSpeed Insights: shows field data (real users) and lab data (a simulated test) for one URL.
  • Chrome DevTools: the Performance panel helps developers find the cause.

Field data is what counts for Google. Lab scores are useful for debugging.

How to improve LCP

  1. Serve images in WebP or AVIF and size them correctly.
  2. Do not lazy-load the main hero image; preload it instead.
  3. Use a fast host and a CDN, and enable caching.
  4. Remove render-blocking CSS and JavaScript.

How to improve INP

  1. Cut unused JavaScript, especially third-party tags and chat widgets.
  2. Break long tasks into smaller chunks.
  3. Delay non-essential scripts until after interaction.

How to improve CLS

  1. Set width and height on images and videos.
  2. Reserve space for ads, embeds and cookie banners.
  3. Load web fonts with font-display: swap and preload key fonts.

Mobile matters most

Mobile scores are usually worse than desktop and they are the ones Google relies on, because of mobile-first indexing. Test on a mid-range phone, not just your laptop.

Frequently asked questions

Why are my scores “not enough data”?

Low-traffic pages lack Chrome user data. Google then groups them with similar pages or uses origin-level data.

Which WordPress plugins help?

Caching and optimisation plugins such as WP Rocket, LiteSpeed Cache or Perfmatters handle many fixes, but a lighter theme often helps most.

Related terms

See site architecture, image optimisation and the SEO encyclopedia.

Mr. SEO is the webmaster at SEO TT - SEO tips and tricks, a publication about all things SEO related.