Core Web Vitals

A set of three Google metrics (LCP, INP, CLS) that measure real-world user experience on loading, interactivity, and visual stability.

Definition

Core Web Vitals (CWV) are standardized metrics focused on three user-centric performance metrics: Largest Contentful Paint (LCP) for loading, Interaction to Next Paint (INP) for responsiveness, and Cumulative Layout Shift (CLS) for visual stability. Google uses CWV as direct ranking signals. Unlike Lighthouse scores which are lab-based, CWV are measured from real-user field data at the 75th percentile.

What Are Core Web Vitals?

Three metrics: LCP (loading, target under 2.5 s), INP (responsiveness, under 200 ms), CLS (visual stability, under 0.1). They replaced older metrics like DOMContentLoaded that did not correlate with human perception.

The 75th Percentile Rule

Google evaluates CWV at the 75th percentile. 75% of users must experience a Good score. A page with median LCP of 2.0 s but p75 of 3.0 s fails.

Common Misunderstandings

CWV is NOT a Lighthouse score. Lighthouse is lab data; CWV is field data from CrUX. A perfect Lighthouse score does not guarantee passing CWV. CWV are evaluated at the URL level, not the site level.

SEO Impact

CWV are a ranking signal. Content relevance dominates, but CWV serve as a tiebreaker. Passing CWV correlates with higher engagement and conversion rates.

Note

INP replaced FID as a Core Web Vital in March 2024.

Common questions

Q: Do I need to pass all three?

A: Yes. Failing even one fails the overall assessment.

Q: Can a slow server pass CWV?

A: Not reliably. TTFB directly feeds into LCP.

Thresholds

Metric: LCP, Good: ≤ 2.5 s, Needs Improvement: 2.5 s - 4.0 s, Poor: > 4.0 s

Metric: INP, Good: ≤ 200 ms, Needs Improvement: 200 ms - 500 ms, Poor: > 500 ms

Metric: CLS, Good: ≤ 0.1, Needs Improvement: 0.1 - 0.25, Poor: > 0.25

Key takeaways:

• Three metrics: LCP, INP, CLS.

• Evaluated at p75 from real-user field data.

• Lighthouse scores are NOT the same as CWV.

• URL-level measurement required.