Core Web Vitals

Core Web Vitals are Google's trio of UX metrics that became ranking signals in 2021. They're not the biggest ranking factor, but they're a tiebreaker and a quality signal.

The three metrics

LCP. Largest Contentful Paint

Time from navigation start until the largest visible element finishes rendering. Measures perceived load speed.

• Good: <2.5 seconds
• Needs improvement: 2.5-4 seconds
• Poor: >4 seconds

INP. Interaction to Next Paint

Measures the worst (or 98th percentile) interaction delay across all of a user's interactions with a page. Replaced FID in 2024.

• Good: <200ms
• Needs improvement: 200-500ms
• Poor: >500ms

CLS. Cumulative Layout Shift

Measures visual stability. Penalizes pages whose content jumps around as it loads.

• Good: <0.1
• Needs improvement: 0.1-0.25
• Poor: >0.25

Why CWV matters (but not as much as some say)

CWV is a ranking factor on the margin. A great page with poor CWV usually still outranks a mediocre page with perfect CWV. But when two pages are close, CWV is a tiebreaker.

Also: poor CWV hurts conversions directly. Users bounce from slow, janky sites. That's the real reason to fix them.

How to measure

• PageSpeed Insights (field + lab data)
• Google Search Console → Core Web Vitals report (field data on your site)
• Chrome User Experience Report (CrUX), real-user data
• Lighthouse, lab-only, useful for iteration

Common fixes

• LCP: optimize images (WebP/AVIF, preload hero image), reduce server response time, defer non-critical JS/CSS
• INP: reduce JS execution, split long tasks, use web workers, defer third-party scripts
• CLS: reserve space for images/ads (width + height), avoid inserting content above existing content, avoid late-loading fonts causing FOUT