Glossary

Core Web Vitals

Three numbers for how a page feels to load, to use and to read.

By Roger Campos · Last updated: September 2026

TL;DR

Core Web Vitals are three metrics Google uses to measure a page's user experience: Largest Contentful Paint (loading, good at 2.5 s or less), Interaction to Next Paint (responsiveness, 200 ms or less) and Cumulative Layout Shift (visual stability, 0.1 or less), each judged at the 75th percentile of real visits.

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What they are

The three metrics

Metric	Measures	Good	Poor
Largest Contentful Paint (LCP)	When the main content has loaded	≤ 2.5 s	> 4.0 s
Interaction to Next Paint (INP)	How quickly the page responds to input	≤ 200 ms	> 500 ms
Cumulative Layout Shift (CLS)	How much content moves unexpectedly	≤ 0.1	> 0.25

Between good and poor is "needs improvement". A page passes when all three are good at the 75th percentile of its real page loads, for mobile and desktop separately. INP replaced First Input Delay as the responsiveness metric in March 2024. Google uses Core Web Vitals as part of its page-experience signals in search ranking.

In practice

Field data vs. lab data

Core Web Vitals are defined on field data: measurements from real visitors' browsers, which Google collects for eligible sites in the Chrome UX Report and shows in Search Console and PageSpeed Insights. Lab data comes from loading the page once in a controlled environment, like Lighthouse. Lab runs are repeatable and work on any page, including one no visitor has seen yet — but they are one load on one simulated device, not the 75th percentile of everyone.

Lab tools measure LCP and CLS directly. INP needs real interactions, so a lab load uses Total Blocking Time as its stand-in.

URLpipe

Measuring them with URLpipe

/lighthouse runs a real Lighthouse audit, mobile by default, and returns LCP, CLS and TBT in metrics with each one's value and score — lab data, on any URL, from outside. It does not return field data; for that, use the Chrome UX Report.

The vitals of one page

curl -s -X POST https://urlpipe.dev/lighthouse \
  -H "Authorization: Bearer YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{"url": "https://example.com", "sync": true}' \
  | jq '.metrics | {lcp: ."largest-contentful-paint".numericValue, cls: ."cumulative-layout-shift".numericValue, tbt: ."total-blocking-time".numericValue}'

The guide to reading a Lighthouse audit explains the rest of the report.

Try it

Core Web Vitals, on a page you choose

Run a Lighthouse audit on any URL

Paste a link and get a real Google Lighthouse audit — performance, accessibility, best practices and SEO scores, plus Core Web Vitals — measured against the live page.

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FAQ

Frequently asked questions

What are the three Core Web Vitals?

Largest Contentful Paint (loading), Interaction to Next Paint (responsiveness) and Cumulative Layout Shift (visual stability).

Are Core Web Vitals a ranking factor?

They are part of Google's page-experience signals. Google describes them as one factor among many; relevant content still matters more.

Why do my Lighthouse results differ from Search Console?

Lighthouse is one lab load on a simulated device; Search Console reports field data from real visitors at the 75th percentile over 28 days. They measure different things and rarely match.

Keep reading

Google Sheets GET /result/:token Parallel requests per plan Run a Lighthouse audit in C#Time to First Byte (TTFB)Cumulative Layout Shift (CLS)All of glossary

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