The Chrome UX Report (CrUX) is a public Google dataset that reflects how real Chrome users experience websites. It includes Core Web Vitals such as LCP, INP and CLS, and it is the dataset of the Web Vitals program. Tools such as PageSpeed Insights draw on it.
At a glance
- Metrics
- Core Web Vitals metrics such as LCP, INP and CLS, plus FCP and TTFB
- Data source
- Field data from real Chrome users
- Assessment
- 75th percentile of page loads (assessment per web.dev)
- Time frame
- 28-day rolling average
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How is the data collected?
CrUX collects data from Chrome on desktop (Windows, macOS, ChromeOS, Linux) and Android, from users who have usage statistics reporting enabled and who sync their browser history without a sync passphrase. Chrome on iOS, Android WebView and other Chromium browsers such as Edge are not included.
A page or origin appears only if it is publicly discoverable (HTTP status 200, no noindex) and has enough visitors. Google does not name the minimum. URL-level data is therefore often missing for low-traffic pages, while origin-level data may exist.
| Metric | Measures | Core Web Vital? | Field or lab | “Good” per web.dev |
|---|---|---|---|---|
| LCP (Largest Contentful Paint) | Render time of the largest image, text block or video visible in the viewport, from the start of navigation | yes (loading) | field and lab | 2.5 s or less |
| INP (Interaction to Next Paint) | Latency of interactions across the whole visit until the next paint; one value that all (or nearly all) interactions fall below | yes (interactivity), since 2024-03-12 | field; in the lab only with simulated interactions, Lighthouse does not measure INP | 200 ms or less |
| CLS (Cumulative Layout Shift) | Largest burst of unexpected layout shifts during the entire lifecycle of the page | yes (visual stability) | field and lab | 0.1 or less |
| TTFB (Time to First Byte) | Time from the start of navigation until the first byte of the response arrives | no (helps diagnose LCP) | field and lab | 0.8 s or less |
| FCP (First Contentful Paint) | Time from the start of navigation until any part of the page's content is rendered | no (helps diagnose LCP) | field and lab | 1.8 s or less |
| TBT (Total Blocking Time) | Total time after FCP during which the main thread was blocked long enough to prevent input responsiveness | no (lab proxy for INP) | lab; web.dev does not recommend field measurement | less than 200 ms on average mobile hardware |
| Speed Index | How quickly content is visually displayed during page load (from a video of the load) | no | lab (Lighthouse) | Threshold according to Lighthouse: mobile up to 3.4 s “fast” (web.dev gives no value) |
| FID (First Input Delay), historical | Time from the first interaction until the browser can begin processing event handlers | until 2024-03-12, replaced by INP | field only | 100 ms or less |
According to web.dev, the 75th percentile of page loads is assessed, mobile and desktop separately. A page passes the Core Web Vitals when LCP, INP and CLS are “good” at the 75th percentile. Chrome tools ended FID support on September 9, 2024. Sources: web.dev: Web Vitals; web.dev: Largest Contentful Paint (LCP); web.dev: Interaction to Next Paint (INP); web.dev: Cumulative Layout Shift (CLS); web.dev: Time to First Byte (TTFB); web.dev: First Contentful Paint (FCP); web.dev: Total Blocking Time (TBT); web.dev: First Input Delay (FID); web.dev Blog: Interaction to Next Paint is officially a Core Web Vital (2024-03-12); Chrome for Developers: Lighthouse – Speed Index. Last checked: .
Time frame and access
The CrUX API returns a 28-day rolling average, updated daily with a delay of about two days. The data is also available through BigQuery, PageSpeed Insights, the CrUX Vis tool and Search Console.
Example
The API takes a POST request with an origin or a URL and an optional form factor:
{ "origin": "https://example.com", "formFactor": "PHONE" }
Sources
- Chrome UX Report – Chrome for Developersdeveloper.chrome.com
- CrUX methodology – Chrome for Developers (last updated 2024-06-20)developer.chrome.com
- CrUX API – Chrome for Developers (last updated 2025-02-11)developer.chrome.com
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