Core Web Vitals: The Complete Guide to LCP, INP, and CLS

Everything you need to know about Google's Core Web Vitals metrics and how to optimize them.

Core Web Vitals: The Complete Guide to LCP, INP, and CLS

What Are Core Web Vitals?

Core Web Vitals are a set of metrics that Google uses to measure real-world user experience on websites. They directly impact your search rankings and represent the most important aspects of page experience.

The Three Core Metrics

LCP (Largest Contentful Paint)

Measures loading performance—how long it takes for the main content to appear.

  • Good: ≤ 2.5 seconds
  • Needs Improvement: 2.5-4 seconds
  • Poor: > 4 seconds

    • INP (Interaction to Next Paint)

    Measures interactivity—how quickly the page responds to user interactions.

  • Good: ≤ 200 milliseconds
  • Needs Improvement: 200-500 milliseconds
  • Poor: > 500 milliseconds

    • CLS (Cumulative Layout Shift)

    Measures visual stability—how much the page layout shifts unexpectedly.

  • Good: ≤ 0.1
  • Needs Improvement: 0.1-0.25
  • Poor: > 0.25

    • How Google Measures Core Web Vitals

    Field Data vs Lab Data

    Field Data (Real User Metrics)

  • Collected from actual users via Chrome UX Report (CrUX)
  • Represents real-world experience
  • Used for search ranking

    • Lab Data

  • Measured in controlled environment (Lighthouse)
  • Useful for debugging
  • Not used for ranking directly

    • Optimizing LCP

    Common LCP Issues

  • Slow server response (TTFB)
  • Render-blocking resources
  • Slow resource load times
  • Client-side rendering

    • LCP Optimization Strategies

  • Optimize server response time
  • Preload critical resources
  • Use CDN for static assets
  • Optimize images (WebP, proper sizing)

    • Optimizing INP

    What Affects INP?

  • Long JavaScript tasks
  • Main thread blocking
  • Heavy event handlers
  • Third-party scripts

    • INP Optimization Strategies

  • Break up long tasks
  • Use web workers for heavy computation
  • Optimize event handlers
  • Defer non-critical JavaScript

    • Optimizing CLS

    Common CLS Causes

  • Images without dimensions
  • Dynamically injected content
  • Web fonts causing FOIT/FOUT
  • Ads and embeds

    • CLS Optimization Strategies

  • Always include width/height on images
  • Reserve space for dynamic content
  • Use font-display: swap
  • Avoid inserting content above existing content

    • Check your Core Web Vitals with our free analysis tool.