Core Web Vitals
A set of specific factors Google considers important for user experience: Largest Contentful Paint (LCP), First Input Delay (FID), and Cumulative Layout Shift (CLS). Part of Google's page experience ranking signals.
Why It Matters
Core Web Vitals are confirmed Google ranking factors. Poor scores can prevent pages from ranking well, while good scores provide ranking advantages. Beyond rankings, optimizing Core Web Vitals improves user experience, reduces bounce rates, and increases conversions by 10-20% on average.
How It Works
LCP measures loading performance (how quickly main content loads), FID measures interactivity (how quickly page responds to user input), and CLS measures visual stability (how much content shifts during loading). Google assesses these metrics based on real user data and determines if pages provide good user experiences worthy of ranking.
Use Cases
- An e-commerce site fixes LCP by optimizing hero images and critical CSS, reducing load time from 4.2s to 1.8s
- A news site improves FID by deferring non-critical JavaScript, making pages interactive 200ms faster
- A blog eliminates CLS by specifying image dimensions and reserving space for ads, reducing layout shift from 0.35 to 0.05
Best Practices
- Target LCP under 2.5 seconds by optimizing images, server response times, and render-blocking resources
- Achieve FID under 100 milliseconds by minimizing JavaScript, using web workers, and breaking up long tasks
- Keep CLS under 0.1 by setting image/video dimensions, avoiding injected content, and reserving space for ads
- Monitor Core Web Vitals in Google Search Console and PageSpeed Insights monthly
- Use field data (real user measurements) alongside lab data for accurate assessment
- Prioritize mobile optimization as Google uses mobile Core Web Vitals for ranking
Frequently Asked Questions
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