Core Web Vitals

Understanding Core Web Vitals

Core Web Vitals consist of three metrics that Google has confirmed as ranking signals:

Largest Contentful Paint (LCP) measures how quickly the largest visible element (typically a hero image or heading block) finishes rendering. Good LCP is under 2.5 seconds. It reflects the perceived loading speed from the user's perspective.

Interaction to Next Paint (INP) replaced First Input Delay (FID) in March 2024 and measures the responsiveness of your page to user interactions throughout the entire visit, not just the first click. Good INP is under 200 milliseconds. It captures whether your page feels sluggish when users click buttons, type in forms, or interact with elements.

Cumulative Layout Shift (CLS) measures unexpected layout movements during the page's lifetime. Good CLS is under 0.1. It captures the frustrating experience of clicking a button only to have the page shift and cause a misclick. Common causes include images without dimensions, dynamically injected ads, and web fonts that cause text reflow.

Google measures Core Web Vitals using real user data from the Chrome User Experience Report (CrUX), not just lab simulations. This means your actual visitors' experience on their real devices and connections determines your scores.

Why Core Web Vitals Matters

Core Web Vitals are confirmed Google ranking factors as part of the page experience signal. While content relevance and authority remain stronger ranking factors, Core Web Vitals serve as a tiebreaker between pages of similar quality — and in competitive markets, that tiebreaker matters. Pages that fail Core Web Vitals thresholds are at a measurable disadvantage.

Beyond rankings, Core Web Vitals directly impact conversion rates and revenue. Studies consistently show that faster pages convert better. Amazon found that every 100ms of latency cost them 1% in sales. The business case for Core Web Vitals optimization goes well beyond SEO.

Best Practices

• Monitor Core Web Vitals in Google Search Console's Core Web Vitals report, which uses real user data
• Optimize LCP by preloading critical resources, compressing images, and minimizing render-blocking CSS/JS
• Improve INP by reducing JavaScript execution time, breaking up long tasks, and optimizing event handlers
• Fix CLS by setting explicit width and height on all images and embeds, and reserving space for dynamic content
• Test changes using both lab tools (Lighthouse) and field data (CrUX) — lab scores can differ from real-world performance
• Prioritize fixing pages that fail Core Web Vitals thresholds before optimizing pages that already pass