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CORE WEB VITALS & PERFORMANCE

Core Web Vitals: what they measure and how they are judged

Google’s three real-user metrics for loading (LCP), responsiveness (INP) and visual stability (CLS).

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All glossary terms
  • Intermediate level
  • 3 primary sources
  • Reviewed 29 October 2026
At a glanceSEO glossary
  • TopicCore Web Vitals & performanceAlso in Technical SEO
  • LevelIntermediateAssumes the basics of how search works
  • Also calledCWV
  • Sources3 primary sourcesweb.dev, Google Search Central and more
  • Reviewed29 October 2026Re-checked every 6 months
On this page
  1. Quick definition
  2. The metrics and their thresholds
  3. Field data and lab data
  4. Why it matters
  5. How to check it
  6. Common mistakes
  7. Related concepts
  8. Check it on your site
  9. Keep learning
  10. Sources and review

Quick definition

Core Web Vitals are three Google metrics for real-user experience: Largest Contentful Paint (loading), Interaction to Next Paint (responsiveness) and Cumulative Layout Shift (visual stability). A page passes when each metric is in the "good" range for at least 75% of real visits.

The metrics and their thresholds

Assessed at the 75th percentile of page loads, separately for mobile and desktop.
MetricMeasuresGoodNeeds improvementPoor
Largest Contentful Paint (LCP)Loading≤ 2.5 s2.5–4.0 s> 4.0 s
Interaction to Next Paint (INP)Responsiveness≤ 200 ms200–500 ms> 500 ms
Cumulative Layout Shift (CLS)Visual stability≤ 0.10.1–0.25> 0.25

INP replaced First Input Delay (FID) as a Core Web Vital in March 2024. Time to First Byte is a useful diagnostic but not a Core Web Vital.

Field data and lab data

Field data comes from real Chrome users who opted in, collected in the Chrome UX Report (CrUX) over a rolling 28-day window. Search Console‘s Core Web Vitals report and Google’s ranking systems use field data. Lab data comes from a test run in controlled conditions, such as Lighthouse; it is repeatable and good for debugging, but it cannot reproduce your real visitors’ devices and networks, and a page-load test has no user interactions, so it reports Total Blocking Time as a stand-in for INP.

Pages without enough traffic have no field data of their own; Search Console then groups similar URLs, and CrUX may only have origin-level data.

Why it matters

Google uses Core Web Vitals in its page experience signals, but it has said that relevance matters far more: a slow page with the best answer can outrank a fast page with a weaker one. The stronger reason to care is visitors. Slow loading, laggy taps and jumping layouts cost enquiries and sales, especially on mid-range phones and mobile data.

How to check it

  1. Open Search Console’s Core Web Vitals report for groups of URLs failing on mobile and desktop.
  2. Look up field data for key URLs and the whole origin in CrUX-based tools such as PageSpeed Insights.
  3. Reproduce problems in the lab (Lighthouse, browser performance panel) to find causes.
  4. After a fix, allow up to 28 days for the field data window to reflect it.

Common mistakes and misconceptions

  • Myth A Lighthouse score of 100 means you pass Core Web Vitals.

    In fact Lighthouse is a lab test. Passing is judged on field data from real visitors.

  • Myth Passing Core Web Vitals will lift rankings.

    In fact It is one signal among many and rarely outweighs relevance and content quality.

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Sources and review

Written and maintained by Ndovu SEO Labs. First published 29 October 2026. Facts last checked against the sources above on 29 October 2026. How we write and review the glossary.