Core Web Vitals
Core Web Vitals are three metrics Google uses to measure real-world user experience on a web page: how fast the main content loads, how quickly the page responds to interaction, and how stable the layout is while it loads. They are part of Google’s page experience signals.
The three Core Web Vitals
- Largest Contentful Paint (LCP) measures loading. The largest image or text block should appear within 2.5 seconds.
- Interaction to Next Paint (INP) measures responsiveness. The page should respond to clicks, taps and key presses within 200 milliseconds. INP replaced First Input Delay (FID) in 2024.
- Cumulative Layout Shift (CLS) measures visual stability. Unexpected layout movement should score 0.1 or less.
A page passes when at least 75% of real visits meet the “good” threshold for all three metrics.
Field data vs lab data
This distinction confuses many website owners:
- Field data comes from real Chrome users, collected in the Chrome User Experience Report (CrUX). This is what Google uses for rankings and what the Core Web Vitals report in Google Search Console shows. It covers the previous 28 days.
- Lab data comes from a single simulated test, such as Lighthouse in PageSpeed Insights. It is useful for diagnosing problems but does not decide your assessment.
That is why a page can score 95 in PageSpeed Insights and still fail Core Web Vitals. I explain this in detail in why PageSpeed Insights shows Core Web Vitals failed when the performance score is high.
How much do Core Web Vitals affect rankings?
Core Web Vitals are a real but modest ranking factor. Relevance and content quality matter far more; a slow page with the best answer can still outrank a fast page with a weak one. However, when competing pages are similar, better page experience can tip the balance. Faster, more stable pages also convert better and keep visitors longer, which makes the work worthwhile regardless of rankings.
How to check your Core Web Vitals
- Open the Core Web Vitals report in Search Console to see groups of URLs that pass, need improvement or fail, split by mobile and desktop.
- Test individual URLs in PageSpeed Insights; the top section shows field data, the lower section lab data.
- Use Chrome DevTools and the Web Vitals extension to debug specific interactions.
Common fixes
- LCP: optimise and preload the hero image, use a CDN, improve server response time, remove render-blocking CSS and JavaScript.
- INP: reduce heavy JavaScript, break up long tasks, limit third-party scripts such as chat widgets and trackers.
- CLS: set width and height on images and embeds, reserve space for ads and banners, load fonts carefully. See my guide on how to fix a CLS issue of more than 0.25 on mobile.
After you fix issues
Because field data covers 28 days, improvements take up to a month to appear in Search Console. Use the “Validate fix” button to track progress, and keep checking after adding new plugins, scripts or design changes, which often reintroduce problems. For broader speed work, see Page Speed.
Further reading: Google on Core Web Vitals and search.
Key Takeaways
- Core Web Vitals measure loading (LCP), responsiveness (INP) and stability (CLS).
- Google uses real-user field data, not the Lighthouse score.
- They are a modest ranking factor but strongly affect conversions.
- Fixes take up to 28 days to show in Search Console.
- Mobile results are usually the hardest to pass.
Related Terms
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