Core Web Vitals
Also known as: CWV, page experience signals
Core Web Vitals are Google's three measurable page-experience signals: Largest Contentful Paint (LCP) measuring loading speed, Interaction to Next Paint (INP) measuring responsiveness, and Cumulative Layout Shift (CLS) measuring visual stability. Pass thresholds: LCP under 2.5s, INP under 200ms, CLS under 0.1. Real-user measurements via Chrome UX Report (CrUX) are what Google uses for ranking signals.
The three metrics
LCP (Largest Contentful Paint)
Time from page-load start to when the largest visible content element renders. Usually the hero image or hero heading. Target: under 2.5s on 75th percentile of users.
INP (Interaction to Next Paint)
Replaced FID in 2024. Measures the latency between user interaction (click, tap, key press) and the next visible response. Target: under 200ms.
CLS (Cumulative Layout Shift)
Sum of unexpected layout shifts during page lifetime. Caused by images without dimensions, late-loading fonts, asynchronously-injected content. Target: under 0.1.
Why CWV matters
- Ranking signal since 2021 (part of Page Experience update)
- AI Overview eligibility — Google preferentially cites pages that pass CWV
- Conversion correlation — every 100ms of LCP improvement typically lifts conversion 1-2%
- Bounce rate correlates with LCP and CLS performance
Lab vs field data
- Lab data (Lighthouse, PageSpeed Insights synthetic) — useful for development, not the ranking signal
- Field data (Chrome UX Report from real users) — what Google actually uses
Always validate fixes against field data over a 28-day rolling window; lab improvements that don’t translate to field improvements aren’t real wins.
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