Core Web Vitals: The Complete Guide for 2025

Core Web Vitals are Google's way of measuring user experience. If your site fails these metrics, you're losing rankings and customers.

The Three Metrics

LCP (Largest Contentful Paint)

What it measures: How long until the main content is visible.

Target: Under 2.5 seconds

Common causes of poor LCP:

• Unoptimized hero images
• Slow server response times
• Render-blocking JavaScript

Quick fixes:

<!-- Preload critical images -->
<link rel="preload" as="image" href="/hero.webp" />

<!-- Use modern formats -->
<picture>
  <source srcset="/hero.avif" type="image/avif" />
  <source srcset="/hero.webp" type="image/webp" />
  <img src="/hero.jpg" alt="Hero" />
</picture>

INP (Interaction to Next Paint)

What it measures: How responsive your site feels when users interact.

Target: Under 200 milliseconds

Common causes of poor INP:

• Heavy JavaScript execution
• Long-running event handlers
• Third-party scripts blocking the main thread

Quick fixes:

// Bad: Blocks main thread
button.addEventListener('click', () => {
  heavyCalculation(); // 500ms
  updateUI();
});

// Good: Don't block the paint
button.addEventListener('click', () => {
  updateUI(); // Paint first
  requestIdleCallback(() => {
    heavyCalculation();
  });
});

CLS (Cumulative Layout Shift)

What it measures: How much the page layout jumps around.

Target: Under 0.1

Common causes of poor CLS:

• Images without dimensions
• Ads and embeds without reserved space
• Web fonts causing text reflow

Quick fixes:

<!-- Always set dimensions -->
<img src="/photo.jpg" width="800" height="600" alt="Photo" />

<!-- Reserve space for dynamic content -->
<div style="min-height: 250px;">
  <!-- Ad loads here -->
</div>

Testing Your Site

Use these tools to check your Core Web Vitals:

1. PageSpeed Insights - Google's official tool
2. Chrome DevTools - Performance panel
3. Search Console - Real user data

The Priority Order

If you're failing multiple metrics, fix them in this order:

1. CLS first - Usually the quickest wins
2. LCP second - Often requires server-side changes
3. INP last - Needs JavaScript optimization

Real Impact

We've seen sites improve their search rankings within weeks of fixing Core Web Vitals. One e-commerce client saw:

• 23% increase in organic traffic
• 15% improvement in conversion rate
• 40% reduction in bounce rate

The metrics matter because they measure real user experience. Faster sites convert better.

Need help passing Core Web Vitals? Contact us for a free audit of your site.