Core Web Vitals explained for business owners

Core Web Vitals are three measurements Google uses to judge how a page feels to real visitors: how quickly it shows its main content, how quickly it responds, and how stable it is while loading. They’re part of how Google ranks pages, and they track closely with whether visitors stay or leave.

1. Largest Contentful Paint (LCP): how fast it loads

LCP is the time until the biggest thing on the screen, usually the hero image or main heading, appears.

• Good: 2.5 seconds or less
• Needs improvement: up to 4 seconds
• Poor: more than 4 seconds

Common causes of a slow LCP are a large hero image, slow hosting, and CSS or JavaScript that blocks the page from appearing.

2. Interaction to Next Paint (INP): how fast it responds

INP measures how quickly the page reacts when someone taps a button, opens a menu or types in a form. It replaced the older First Input Delay measurement in 2024.

• Good: 200 milliseconds or less
• Needs improvement: up to 500 milliseconds
• Poor: more than 500 milliseconds

A poor INP usually means too much JavaScript running on the page, often from page builders, sliders or third-party scripts.

3. Cumulative Layout Shift (CLS): how stable it is

CLS measures how much the page jumps around while it loads. You’ve felt it when you go to tap a link and an image loads above it, pushing everything down.

• Good: 0.1 or less
• Needs improvement: up to 0.25
• Poor: more than 0.25

The usual causes are images without set dimensions, late-loading banners and fonts that change size as they load.

Lab data and real-visitor data

A speed test gives you lab data: one test, on one simulated phone, at one moment. It’s ideal for finding problems. Google also collects field data from real Chrome users over the last 28 days, and that’s what counts for rankings. Field data only appears once a site has enough visitors.

What about the PageSpeed score?

The 0 to 100 score from PageSpeed Insights is a summary of several lab measurements. 90 and above is good, 50 to 89 needs improvement, and below 50 is poor. It’s a useful single number to track, but the three Core Web Vitals are what Google actually uses.

Check your own site

Run a free speed test to see your score, your Core Web Vitals and the fixes that would help most. If the numbers are red, I can help.