Chrome UX Report (CrUX) & Real-User Metrics
CrUX reports real-user performance over a collection window. Use it alongside lab diagnostics.
Ludwig Makhyan · Founder, WebsiteCoach ·
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Executive Overview
Check whether the data describes a URL or the whole origin, which device group it covers, and its collection dates. The 75th percentile is not an average. Missing data may mean insufficient eligible traffic.
Business Impact
Core Web Vitals contribute to Google's ranking systems, but do not guarantee positions or explain a ranking change on their own.
Source: Google Chrome UX Report API — 28-day rolling window, 75th percentile.
Key Metrics Explained
- LCP at 75th percentile (p75)
- Field loading performance. A p75 LCP of 2.5 seconds or less is good; investigate the main content element if it is slower.
- INP — Interaction to Next Paint (p75)
- Field responsiveness across interactions. A p75 INP of 200 ms or less is good. Inspect slow interactions and main-thread work.
- CLS at 75th percentile (p75)
- Field visual stability. A p75 CLS of 0.1 or less is good. Look for content that shifts during a visit.
- FCP & TTFB from real users
- FCP measures the first visible content; TTFB measures the wait for the first response byte. Both aid diagnosis but are not Core Web Vitals.
- Good / Needs Improvement / Poor ratings
- Ratings classify each metric against its thresholds. Missing field data is unavailable evidence, not a poor rating.
- Aggregated across all form factors
- A combined device view can hide a mobile problem. Compare the same device scope and collection period whenever possible.
CrUX vs Lab Data — What's the Difference?
Lab diagnostics (Lighthouse)
- • A controlled test with configured device and network conditions
- • Controlled network and device conditions
- • Can test reachable pages without a CrUX traffic history
- • Good for diagnosing specific issues
- • Does NOT influence rankings directly
Field Data (CrUX)
- • Real Chrome users on real devices
- • A 28-day collection window in the CrUX API
- • Requires sufficient traffic to populate
- • Reflects actual user experience
- • Core Web Vitals contribute to Google's ranking systems, but do not guarantee positions or explain a ranking change on their own.
Role-Specific Action Plan
- →Review CrUX ratings vs lab scores — gaps indicate real-user problems not caught in testing
- →Include CrUX 'Good' status as a product release criterion
- →Monitor TTFB from real users — CDN misses or cold starts often only show in CrUX
- →Ensure geographic CDN coverage matches your user base
- →Investigate discrepancies between lab LCP and CrUX LCP — often caused by dynamic content, A/B tests, or personalisation
- →Profile INP by auditing event handler execution time using Chrome DevTools
- →Monitor CrUX status in Google Search Console > Core Web Vitals report
- →Core Web Vitals contribute to Google's ranking systems, but do not guarantee positions or explain a ranking change on their own.
How to check Chrome UX Report data
- Open PageSpeed Insights and enter the page URL. Read the real-user experience section separately from the Lighthouse diagnostic test.
- Check whether the result describes this URL or the origin. Origin data combines eligible experiences across the website and is not a measurement of this page alone.
- Record the collection period and device selection. Compare mobile with mobile and URL data with URL data when measuring a change.
- Use the field result to choose what to investigate, then use Lighthouse or a browser performance recording to locate a possible cause. Recheck field data after new visits enter the reporting window.
Worked example: read the 75th percentile
Illustrative mobile results for a 28-day period are shown below. At p75, 75% of the recorded experiences have a value at or below the reported value. This is not the arithmetic average.
| Metric | Example p75 | Interpretation and next check |
|---|---|---|
| LCP | 3.2 seconds | Needs improvement. Investigate the main content element, its request timing, and render delays. |
| INP | 180 milliseconds | Good. Preserve responsiveness while making other changes. |
| CLS | 0.14 | Needs improvement. Look for late content insertion and missing space for images or embeds. |
Why CrUX can be missing or disagree with Lighthouse
Missing field data can mean the page or origin does not have enough eligible traffic, or does not meet discoverability requirements. Google does not publish an exact visitor threshold. Missing data is not a failing performance grade.
A fast lab test and slow field results can coexist: real visitors use different devices, networks, locations, and page states. CrUX also includes experiences from before a recent release within its reporting window. Keep the tested URL, device, and scope consistent before comparing results.
Core Web Vitals are used by Google's ranking systems, but they do not explain a ranking change on their own. FCP and TTFB are useful diagnostics; TBT is a lab metric, not a Core Web Vital.
Frequently asked questions
What is Chrome UX Report (CrUX) & Real-User Metrics?
CrUX reports real-user performance over a collection window. Use it alongside lab diagnostics.
Why does Chrome UX Report (CrUX) & Real-User Metrics matter?
Core Web Vitals contribute to Google's ranking systems, but do not guarantee positions or explain a ranking change on their own.
Official references
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