Core Web Vitals Score Calculator

Drop in the metric values from Lighthouse, PageSpeed Insights, CrUX, or your own RUM and see which ones pass Google's official thresholds — and which page experience signal will sink your search ranking. The three Core Web Vitals (LCP, INP, CLS) must all be Good for a URL to count as passing.

Try:

What needs to improve

A focused checklist for the metric that's failing — the highest-impact things to try first.

Official thresholds (75th percentile of page loads)

A metric is Good only when the 75th-percentile value across mobile and desktop hits the Good threshold. Above the Poor cutoff it's Poor; in between it's Needs Improvement. These thresholds come from web.dev/vitals (March 2024 INP migration).

Metric	What it measures	Good	Needs improvement	Poor
LCP	Largest Contentful Paint — time to render the largest visible element	≤ 2.5 s	2.5 – 4.0 s	> 4.0 s
INP	Interaction to Next Paint — slowest interaction latency (replaced FID in Mar 2024)	≤ 200 ms	200 – 500 ms	> 500 ms
CLS	Cumulative Layout Shift — sum of layout shift scores over the session window	≤ 0.1	0.1 – 0.25	> 0.25
FCP	First Contentful Paint — time until any text or image renders	≤ 1.8 s	1.8 – 3.0 s	> 3.0 s
TTFB	Time to First Byte — time until the first response byte arrives	≤ 0.8 s	0.8 – 1.8 s	> 1.8 s
FID (legacy)	First Input Delay — replaced by INP on March 12, 2024	≤ 100 ms	100 – 300 ms	> 300 ms

Notes & FAQs

Why the 75th percentile? A site passes a Core Web Vital only when 75% of real-user visits hit the Good threshold. A median ("typical") visit doing fine isn't enough — the long tail counts.
Lab vs field. Lighthouse (lab) gives you a single number; CrUX (field) gives you the percentile of your real users. The thresholds are identical; the inputs aren't. Use CrUX p75 values when comparing to "passing".
INP vs FID. FID only measured the first interaction's delay, missing pages that get sluggish later. INP looks at the worst (or near-worst) interaction across the whole visit. INP replaced FID in Core Web Vitals on March 12, 2024.
CLS session window. Modern CLS sums shifts within a 5-second window with a 1-second gap, then reports the worst window — not the lifetime total. Late shifts after user input are excluded.
Mobile vs desktop. Google ranks pages using mobile-first CrUX data. Desktop scores can be much greener — don't let the desktop pass mask a failing mobile score.