Interactive Tool
Core Web Vitals Score Explainer
Enter the scores from your PageSpeed Insights report. The tool will explain what each number means, how you compare to the web, and what to fix first.
Enter your scores
Copy these values from PageSpeed Insights, Google Search Console, or Chrome DevTools Lighthouse. Use the p75 field data when available; otherwise use lab data.
Understanding PageSpeed Insights results
PageSpeed Insights (PSI) provides two types of data for your URL. Understanding the difference is critical to diagnosing performance issues correctly.
Field data vs. lab data
Field data (also called "real-user data" or CrUX data) comes from actual Chrome users who visit your site. It represents what real people experience across different devices, networks, and locations. Field data is what Google uses for search ranking signals. If your site has enough traffic, PSI shows field data at the top of the report.
Lab data comes from Lighthouse, which simulates a page load under controlled conditions (a mid-tier mobile device on a throttled 4G connection). Lab data is useful for debugging specific issues, but it does not directly represent real user experience. A site can have excellent lab scores but poor field scores (or vice versa).
The 75th percentile rule
Core Web Vitals are evaluated at the 75th percentile (p75) of all page views. This means 75% of your users must have a "good" experience for the metric to pass. This is intentionally stricter than using the median (p50) because it accounts for the long tail of slower experiences caused by older devices, poor connections, and geographic distance from your servers.
What "Good", "Needs Improvement", and "Poor" mean
| Metric | Good | Needs Work | Poor |
|---|---|---|---|
| LCP | ≤ 2.5s | 2.5 -- 4.0s | > 4.0s |
| INP | ≤ 200ms | 200 -- 500ms | > 500ms |
| CLS | ≤ 0.10 | 0.10 -- 0.25 | > 0.25 |
| TTFB | ≤ 800ms | 800 -- 1800ms | > 1800ms |
Common misconceptions
- "My Lighthouse score is 95, so I'm fine." Lighthouse scores do not directly reflect field performance. A 95 lab score with poor field data means real users are having a bad experience, and that is what Google ranks on.
- "I optimized my site and nothing changed." Field data in CrUX updates on a 28-day rolling window. After making improvements, wait 28 days to see changes in PageSpeed Insights field data. Use Lighthouse for immediate feedback during development.
- "My LCP is fine on my fast computer." Core Web Vitals are measured at the 75th percentile on real devices, which includes older phones on cellular networks. Test with Chrome DevTools device emulation set to "Mid-tier mobile" with "Slow 4G" throttling for a realistic picture.
- "CLS is zero in Lighthouse but high in the field." Lighthouse measures CLS during page load only. Field CLS also captures layout shifts caused by user interactions, late-loading ads, cookie banners, and dynamically inserted content that only appears after the initial load.
Frequently asked questions
What are Core Web Vitals?
Core Web Vitals are a set of three metrics defined by Google that measure real-world user experience on web pages: Largest Contentful Paint (LCP) measures loading speed, Interaction to Next Paint (INP) measures interactivity and responsiveness, and Cumulative Layout Shift (CLS) measures visual stability. These metrics are used as ranking signals in Google Search.
What is a good LCP score?
A good LCP score is 2.5 seconds or less. LCP between 2.5 and 4.0 seconds needs improvement, and LCP above 4.0 seconds is poor. LCP measures when the largest visible content element (typically a hero image or heading) finishes rendering.
What is a good INP score?
A good INP score is 200 milliseconds or less. INP between 200 and 500 milliseconds needs improvement, and INP above 500 milliseconds is poor. INP measures the responsiveness of a page by observing the latency of all click, tap, and keyboard interactions throughout the page lifecycle.
What is a good CLS score?
A good CLS score is 0.1 or less. CLS between 0.1 and 0.25 needs improvement, and CLS above 0.25 is poor. CLS measures visual stability by quantifying how much visible content shifts during page load and interaction.
Where can I find my Core Web Vitals scores?
You can find your Core Web Vitals scores in several places: Google PageSpeed Insights (pagespeed.web.dev) shows both lab and field data. Google Search Console reports field data under the Core Web Vitals section. Chrome DevTools Lighthouse panel provides lab measurements. The Chrome User Experience Report (CrUX) API provides field data for sites with sufficient traffic.