Core Web Vitals

Google's set of real-world performance metrics — LCP, INP, and CLS — that measure page loading, interactivity, and visual stability.

Definition

Core Web Vitals (CWV) are a subset of Google's Web Vitals initiative: a set of standardized, user-centric performance metrics that Google uses as ranking signals as part of the Page Experience update. The three Core Web Vitals are: Largest Contentful Paint (LCP), which measures loading performance; Interaction to Next Paint (INP), which replaced First Input Delay in March 2024 and measures responsiveness to all user interactions; and Cumulative Layout Shift (CLS), which measures visual stability.

Target thresholds: LCP should be under 2.5 seconds (good) or 4.0 seconds (needs improvement); INP should be under 200ms (good) or 500ms (needs improvement); CLS should be under 0.1 (good) or 0.25 (needs improvement). Pages that meet "good" thresholds for all three metrics benefit from a ranking boost in Google's Page Experience signal.

CWV data is collected from real Chrome users (the Chrome User Experience Report, or CrUX dataset) for sites with sufficient traffic, and from Lighthouse lab data for pages without sufficient field data. Common improvements: optimize image formats and sizes for LCP, defer JavaScript and use event delegation for INP, and add explicit dimensions to images and embeds to prevent layout shifts for CLS. Monitor CWV in Google Search Console's "Core Web Vitals" report.

Frequently Asked Questions

How much do Core Web Vitals affect Google rankings?

Google has confirmed CWV as a ranking signal, but it's a tiebreaker signal rather than a dominant one. Google's documentation states that 'great page experience doesn't override having great page content.' Fix CWV to eliminate a ranking disadvantage, not as a substitute for quality content.

What is the difference between lab data and field data for CWV?

Lab data (from Lighthouse/PageSpeed Insights) is simulated under controlled conditions on a test device. Field data (from CrUX) reflects real user experiences across all their devices and connections. Google uses field data for ranking when available. Lab data is useful for debugging but may not match the actual ranking signal.