Glossary · Definition
Core Web Vitals
Core Web Vitals are three Google-defined metrics that measure the real-user experience of a web page: LCP (loading), INP (interactivity), and CLS (visual stability). They're a direct ranking signal as of 2021.
Definition
Core Web Vitals are three Google-defined metrics that measure the real-user experience of a web page: LCP (loading), INP (interactivity), and CLS (visual stability). They're a direct ranking signal as of 2021.
What it means
Google introduced Core Web Vitals as part of Page Experience — the acknowledgment that fast, stable pages should rank better than slow, janky ones. The three metrics are measured on real user sessions (via CrUX, the Chrome User Experience Report) and summarized into 'Good', 'Needs Improvement', and 'Poor' categories. LCP (Largest Contentful Paint) measures loading — the time until the largest visible element renders. INP (Interaction to Next Paint, replacing FID in 2024) measures interactivity — how quickly the page responds to taps and clicks. CLS (Cumulative Layout Shift) measures visual stability — how much the page jumps around as it loads.
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Formula
LCP target: ≤ 2.5s (75th percentile) INP target: ≤ 200ms (75th percentile) CLS target: ≤ 0.1 (75th percentile)
Why it matters
Core Web Vitals directly influence rankings, especially as a tiebreaker between pages of similar topical quality. More importantly, they correlate with bounce rate — slow pages lose users regardless of ranking. Hitting 'Good' on all three is a competitive table stake. Falling into 'Poor' on any one can tank rankings for pages that otherwise should perform well.
Frequently asked questions
Are Core Web Vitals desktop or mobile?
Both are measured, but mobile is the primary signal — Google's index has been mobile-first since 2019.
How is this measured?
On real user sessions, aggregated into the Chrome User Experience Report (CrUX). Synthetic tests like Lighthouse estimate the same metrics but don't replace CrUX for ranking.
What replaced FID?
INP (Interaction to Next Paint) replaced FID (First Input Delay) in March 2024. INP measures interaction latency across the whole session, not just the first input.
Related terms
- DefinitionLCPLCP (Largest Contentful Paint) is the time from when a page starts loading to when the largest visible content element finishes rendering. Google's target is 2.5 seconds or less on the 75th percentile.
- DefinitionCLSCLS (Cumulative Layout Shift) measures how much visible content jumps around unexpectedly as a page loads. Google's target is 0.1 or less. It's the metric that scores how 'janky' a page feels.