Core Web Vitals Explained: What They Mean for Your Website

Core Web Vitals are Google's way of measuring the user experience of a website. Since 2021, they have officially been a ranking factor. The better you score, the more favorably Google treats you. But what exactly do they measure?

What are Core Web Vitals?

Core Web Vitals are three specific metrics that together measure the loading experience of a web page:

1. LCP - Largest Contentful Paint (loading speed)
2. INP - Interaction to Next Paint (interactivity)
3. CLS - Cumulative Layout Shift (visual stability)

Note: INP replaced FID (First Input Delay) in March 2024

LCP: Largest Contentful Paint

What does it measure?

LCP measures how long it takes for the largest visible element on the page to load. This is usually:

• A hero image
• A large text block
• A video thumbnail

It is about what the user sees, not what is technically loading.

What are good scores?

| Score | Rating | |-------|--------| | ≤ 2.5 sec | Good | | 2.5 - 4 sec | Needs Improvement | | > 4 sec | Poor |

How to improve LCP?

Optimize server response time:

• Choose faster hosting
• Use a CDN
• Implement caching

Eliminate render-blocking resources:

• Defer non-critical JavaScript
• Inline critical CSS
• Preload important resources

Optimize images:

• Compress images
• Use modern formats (WebP, AVIF)
• Implement lazy loading
• Specify width and height attributes

Optimize fonts:

• Host fonts locally
• Use font-display: swap
• Preload important fonts

INP: Interaction to Next Paint

What does it measure?

INP measures how quickly the website responds to user interactions. It looks at all interactions during a visit (clicks, taps, keystrokes) and reports the worst experience.

This replaces FID, which only measured the first interaction.

What are good scores?

| Score | Rating | |-------|--------| | ≤ 200 ms | Good | | 200 - 500 ms | Needs Improvement | | > 500 ms | Poor |

How to improve INP?

Optimize JavaScript:

• Break up long tasks
• Defer non-essential scripts
• Use web workers for heavy tasks
• Remove unused code

Limit third-party scripts:

• Audit all external scripts
• Load them async or defer
• Consider alternatives

Optimize event handlers:

• Use throttling/debouncing
• Minimize DOM manipulations
• Optimize event listeners

CLS: Cumulative Layout Shift

What does it measure?

CLS measures how much the page "jumps" during loading. You know the scenario: you want to click a link, but suddenly everything shifts because an ad loads, and you click on the wrong thing.

What are good scores?

| Score | Rating | |-------|--------| | ≤ 0.1 | Good | | 0.1 - 0.25 | Needs Improvement | | > 0.25 | Poor |

How to improve CLS?

Specify dimensions:

• Always give width and height to images
• Use aspect-ratio for responsive images
• Reserve space for embeds

Fonts:

• Use font-display: optional or swap
• Match fallback font to webfont
• Preload important fonts

Ads and embeds:

• Reserve space for ads
• Use placeholders
• Do not load dynamically above existing content

Animations:

• Only animate transform and opacity
• Avoid layout-triggering properties
• Use will-change sparingly

How to measure Core Web Vitals?

Field data (real users)

Google Search Console:

• Core Web Vitals report
• Provides overview of all pages
• Shows trends over time

PageSpeed Insights:

• Uses Chrome User Experience Report
• Real data from Chrome users
• Free to use

Web Vitals JavaScript library:

• Measure in your own analytics
• Real-user monitoring

Lab data (simulated)

Lighthouse:

• Built into Chrome DevTools
• Provides specific advice
• Simulation, not real users

WebPageTest:

• Extensive test options
• Filmstrip of loading
• Waterfall analysis

Difference between field vs lab

• Field data is what Google uses for rankings
• Lab data is useful for debugging
• Scores can differ (lab vs real world)

Impact on SEO

Direct ranking factor

Core Web Vitals are one of many ranking factors. Google has stated that content relevance is still more important, but with equal relevance, the faster site wins.

Page Experience signals

Core Web Vitals are part of broader Page Experience signals:

• Core Web Vitals (LCP, INP, CLS)
• Mobile-friendliness
• HTTPS
• No intrusive interstitials

Practical impact

For competitive keywords: If you and a competitor have comparable content, better Core Web Vitals can make the difference.

For local search results: Google only shows sites with good experience in the 3-pack.

In Google Discover: Poor Core Web Vitals can exclude you from Discover.

Setting priorities

Not all pages are equally important. Focus first on:

1. Homepage - Often most visited
2. Landing pages - Where campaigns land
3. Product pages - Critical for conversion
4. Blog posts with high traffic - High volume

Gradual improvement

You do not need to fix everything at once:

1. Measure your current status
2. Identify the biggest problems
3. Fix the easy wins first
4. Measure again
5. Address the next issues

Common issues and solutions

Issue: Slow LCP due to large hero image

Solution:

<img
  src="hero.webp"
  width="1200"
  height="600"
  fetchpriority="high"
  alt="Hero"
/>

Issue: CLS from late font loading

Solution:

@font-face {
  font-family: 'CustomFont';
  font-display: swap;
  src: url('font.woff2') format('woff2');
}

Issue: Poor INP due to heavy JavaScript

Solution:

• Split code with dynamic imports
• Lazy load non-critical components
• Optimize event handlers

Tools that help

• Squoosh: Image compression
• SVGOMG: SVG optimization
• Bundlephobia: Check npm package size
• Lighthouse CI: Automated testing
• Calibre/SpeedCurve: Monitoring over time

Conclusion

Core Web Vitals are not just metrics - they measure real user experience. A fast, stable website is better for your visitors and for your rankings.

Start by measuring, identify your biggest problems, and tackle them one by one. Perfection is not necessary; improvement is.

Want to know how your website scores? Contact us for a free Core Web Vitals analysis.

Further reading

• Website Performance Optimization - Comprehensive guide to faster websites
• Faster Website with Cloudflare CDN - Improve your LCP with a CDN
• Technical SEO Checklist - Core Web Vitals in SEO context
• Getting Started with SEO - The basics of search engine optimization