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SEO · Performance

Core Web Vitals: why site speed matters to your customers and to Google

What LCP, INP and CLS measure, which values to aim for and where to start to make your website faster, without unnecessary jargon.

by Published on 2 min read

A slow website costs you twice: people leave before they read, and Google has one less reason to show it. Core Web Vitals are the three metrics Google uses to measure the real experience of people visiting a page, and they are worth understanding even if you are not technical.

The three metrics, in plain words

LCP (Largest Contentful Paint) measures how long it takes for the main element of the page to appear, usually a large image or the headline. It is the feeling that “the page has loaded”.

INP (Interaction to Next Paint) measures how quickly the page responds when you tap a button, open a menu or fill in a field. It replaced the older FID metric in 2024.

CLS (Cumulative Layout Shift) measures how much elements move around while the page loads: the classic button that slides away just as you are about to tap it.

The values to aim for

Google considers an experience good when, for at least 75% of visits:

Metric Good Needs improvement Poor
LCP ≤ 2.5 s 2.5 to 4 s > 4 s
INP ≤ 200 ms 200 to 500 ms > 500 ms
CLS ≤ 0.1 0.1 to 0.25 > 0.25

This data comes from real users and is assessed separately for phones and desktops: a site that flies on an office computer can be slow on a mobile connection.

Do they matter for SEO?

Yes, but not on their own. Relevance and content quality remain the main factor; when content is comparable, though, a better experience helps. Above all, it matters to people: a page that loads immediately and doesn’t “jump” gets read more and brings in more enquiries.

Where to start

  1. Measure. Open PageSpeed Insights and enter your site’s address. If the site has enough visits you will see real-user data; otherwise, a lab simulation.
  2. Check Search Console. The “Core Web Vitals” report shows which groups of pages have problems.
  3. Fix your images. Modern formats (WebP, AVIF), sizes that match the screen and never lazy-loading the main image solve most LCP problems.
  4. Reserve space. Declaring image and video dimensions and reserving room for banners and late-loading content prevents the shifts that hurt CLS.
  5. Trim the JavaScript. Plugins, widgets and third-party scripts are the most common cause of a poor INP.

If you want to know how your site is doing, we can run a check and point out the priorities, even if we didn’t build the site.

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