Core Web Vitals explained for business owners

Core Web Vitals are three measurements Google uses to judge how a page feels to a real visitor: how fast it shows its main content, how quickly it responds when tapped, and how stable it stays while loading. They're part of Google's page experience signals, and more importantly they track closely with whether visitors stay or leave.

You don't need to be a developer to understand them. Here's what each one means, what a good score is, and what usually needs fixing.

LCP: how fast does the main content appear?

Largest Contentful Paint measures when the biggest image or block of text in the visible part of the screen finishes rendering. It's the moment a visitor feels the page has loaded.

• Good: 2.5 seconds or less.
• Needs improvement: 2.5 to 4 seconds.
• Poor: over 4 seconds.

Common causes of a slow LCP are oversized hero images, slow hosting, sliders and video backgrounds, web fonts that block text from appearing, and scripts that must load before anything is shown.

INP: how quickly does the page respond?

Interaction to Next Paint measures the delay between a visitor's tap, click or key press and the page visibly reacting. It replaced an older metric, First Input Delay, in March 2024, and it's stricter because it looks at interactions throughout the visit, not just the first.

• Good: 200 milliseconds or less.
• Needs improvement: 200 to 500 milliseconds.
• Poor: over 500 milliseconds.

Heavy JavaScript is almost always the cause: page builders, plugins, chat widgets, tracking tags and third-party embeds all compete for the phone's processor.

CLS: how much does the page jump around?

Cumulative Layout Shift measures unexpected movement while the page loads. You've felt it: you go to tap a button and an image loads above it, pushing the button away.

• Good: 0.1 or less.
• Needs improvement: 0.1 to 0.25.
• Poor: over 0.25.

Typical causes are images and videos without set dimensions, ads and embeds that load late, cookie banners that push content down, and web fonts that swap in with different widths. On this website we matched the fallback font widths to our real fonts so headings don't rewrap when the fonts arrive.

Lab data vs field data: which scores count?

There are two kinds of measurement. Lab data comes from a test run on demand, such as Lighthouse or PageSpeed Insights, on a simulated phone. It's great for finding problems. Field data comes from real Chrome users visiting your site over the past 28 days, collected in the Chrome UX Report. Google uses field data, and a page passes when at least 75% of visits meet the good threshold for each metric.

Smaller sites may not have enough visits for field data. In that case, aim for good lab scores on a mobile test, since that's your best predictor.

Where to check your scores

• Google Search Console: the Core Web Vitals report groups your pages into good, needs improvement and poor, using field data.
• PageSpeed Insights: test any single page and see both field data (if available) and a lab report with suggestions.
• Chrome DevTools: developers can record a page load and see exactly what delays each metric.

Do Core Web Vitals affect rankings?

Yes, but modestly. Google has said relevance and helpful content come first, and page experience helps decide between pages of similar quality. The bigger effect is on visitors: slow, jumpy pages lose people before they read a word, and that costs enquiries regardless of rank.

What usually gets the biggest improvement?

1. Compress and correctly size images, and use modern formats such as WebP or AVIF.
2. Remove plugins, widgets and tags you don't need, and delay the rest until after the page loads.
3. Move to faster hosting with caching and HTTP/2 or HTTP/3.
4. Preload the main image and fonts, and give every image set dimensions.
5. Replace heavy page builders with a lighter, purpose-built site when a rebuild is due.

Our web design projects are built to pass Core Web Vitals on mobile, and we can audit an existing site and tell you what's worth fixing. See also how to speed up a slow website.