What are Core Web Vitals
Core Web Vitals are a set of three key performance metrics that Google uses to evaluate the user experience on web pages. Since May 2021, Core Web Vitals have been official Google ranking factors.
The three metrics:
- LCP (Largest Contentful Paint) — how quickly the main content loads
- INP (Interaction to Next Paint) — responsiveness to user interactions
- CLS (Cumulative Layout Shift) — visual stability of the page
Google measures these metrics using real user data (Chrome User Experience Report, CrUX), not lab tests.
Why Core Web Vitals matter
Direct impact on SEO: Google uses CWV as one of the Page Experience ranking signals. All else being equal, a site with good CWV has an advantage.
Improved conversions: The BBC found that every 0.1s faster loading increases conversions by 1%. Google Shopping: improving CLS by 0.1 increased sales by 1%.
Fewer bounces: 53% of mobile users leave a site if it takes more than 3 seconds to load.
Core Web Vitals metrics
LCP — Largest Contentful Paint
The time it takes for the largest visible element (an image, block of text, or video) to load.
| Value | Rating |
|---|---|
| up to 2.5 s | Good |
| up to 4.0 s | Needs improvement |
| more than 4.0 s | Poor |
How to improve LCP:
- Optimize images (WebP, compression, lazy loading)
- Use a CDN for static assets
- Preload critical resources using link rel preload
- Eliminate render-blocking CSS and JavaScript
INP — Interaction to Next Paint
Page responsiveness: the time from a user interaction (click, tap) to the screen update. It replaced FID in March 2024.
| Value | Rating |
|---|---|
| up to 200 ms | Good |
| up to 500 ms | Needs improvement |
| more than 500 ms | Poor |
How to improve INP:
- Break up long JavaScript tasks
- Avoid blocking operations in event handlers
- Optimize DOM manipulations
- Use Web Workers for heavy computations
CLS — Cumulative Layout Shift
A measure of unexpected shifts in page elements as the page loads.
| Value | Rating |
|---|---|
| up to 0.1 | Good |
| up to 0.25 | Needs improvement |
| more than 0.25 | Poor |
How to improve CLS:
- Specify image and video dimensions (width/height attributes)
- Avoid inserting content above existing content (banners, notifications)
- Preload fonts and use font-display swap
- Reserve space for dynamic content
How to measure Core Web Vitals
- Google Search Console — Core Web Vitals (real user data)
- PageSpeed Insights — lab and field data
- Chrome DevTools — Performance tab
- Lighthouse — built into Chrome DevTools
Check Core Web Vitals with reChecker
Use Web Vitals to analyze your metrics. The tool shows:
- Current LCP, INP, and CLS values
- A rating for each metric (good/needs improvement/poor)
- Specific recommendations for improvement
- A comparison with Google's thresholds
FAQ
Are Core Web Vitals required to reach the top of search results? No, they are just one of more than 200 ranking factors. Poor CWV won't prevent a site with very strong content and backlink profile from ranking highly. But all else being equal, good CWV can help.
What is the difference between lab and field data? Lab data (PageSpeed Insights, Lighthouse) comes from a synthetic test in controlled conditions. Field data (CrUX, Search Console) is real user data from the past 28 days. Google uses field data for ranking.
What changed when INP replaced FID? FID measured only the time to the first interaction. INP measures all interactions on the page and uses the 98th percentile, which better reflects overall responsiveness. The thresholds became stricter.