What are the Core Web Vitals thresholds?

LCP is Good at 2500 ms or less and Poor above 4000 ms. INP is Good at 200 ms or less and Poor above 500 ms. CLS is Good at 0.1 or less and Poor above 0.25. Anything between the Good and Poor cut-offs is Needs Improvement.

Why did INP replace FID?

First Input Delay only measured the delay before the first interaction was processed, not the full time to the next paint, and only the first interaction. Interaction to Next Paint (INP) measures the worst-case latency across all interactions through to the visual update, which better reflects responsiveness. INP became a Core Web Vital in March 2024.

How do I measure these metrics?

Use the PerformanceObserver API or the web-vitals JavaScript library in the field for LCP, INP, CLS, FCP and TTFB. Lab tools like Lighthouse and PageSpeed Insights also report them, but lab INP and CLS can differ from field data because real interaction patterns are not simulated.

Are FCP and TTFB Core Web Vitals?

No. FCP (First Contentful Paint) and TTFB (Time to First Byte) are diagnostic metrics that help explain a poor LCP, but only LCP, INP and CLS are the three Core Web Vitals that affect search ranking. FID is now deprecated in favor of INP.

Web Vitals Thresholds Reference

Q: What percentile does Google use to grade a page?

Google assesses each metric at the 75th percentile of real-user field data, segmented across mobile and desktop. A page passes Core Web Vitals only when LCP, INP and CLS are all in the Good range at that percentile, so a few slow sessions will not fail an otherwise fast page.

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Web Vitals are Google’s standardized metrics for loading, interactivity and visual stability, and each one has fixed thresholds that sort a measurement into Good, Needs Improvement or Poor. Mixing up the cut-offs — or the units — leads to chasing the wrong number. This reference lists every threshold and lets you paste a measured value to see exactly which bucket it lands in.

How it works

Each metric has two cut-offs. A value at or below the Good threshold is good; a value above the Poor threshold is poor; anything in between is Needs Improvement. The three Core Web Vitals are LCP (loading — Good ≤ 2500 ms), INP (interactivity — Good ≤ 200 ms) and CLS (visual stability — Good ≤ 0.1, a unitless score). The diagnostic metrics FCP (Good ≤ 1800 ms) and TTFB (Good ≤ 800 ms) help explain a slow LCP, while FID is the deprecated predecessor of INP.

Crucially, Google grades a real page at the 75th percentile of field data collected from actual users, split between mobile and desktop. A page passes Core Web Vitals only when LCP, INP and CLS are all Good at that percentile, so the occasional slow session will not fail a page that is fast for most visitors.

Tips and notes

Measure in the field, not just the lab: lab tools like Lighthouse cannot simulate real interaction patterns, so lab INP and CLS often differ from what users experience. Use the PerformanceObserver API or the web-vitals library to capture field values, and remember that CLS is a unitless score while every other metric here is measured in milliseconds.