Core Web Vitals field data (Chrome UX Report)
Field data is performance measured on real visits, by real people, on their own devices and networks. Google collects it through the Chrome UX Report (CrUX) from Chrome users who have opted in to sharing usage statistics, and publishes it as a rolling 28-day summary. PageSpeed Insights returns this data alongside the lab test, and we show it when it exists.
The Core Web Vitals are three field metrics:
- Largest Contentful Paint (LCP): loading speed.
- Interaction to Next Paint (INP): responsiveness.
- Cumulative Layout Shift (CLS): visual stability.
This guide covers field LCP and field CLS; INP has its own guide.
Why it matters
Lab tests run one page load on one simulated device. Field data reflects what your visitors actually experienced, across every device, network and location they used. It is also the data Google uses for its page experience signals in Search. When lab and field disagree, field data is the one that describes reality.
What we check
PageSpeed Insights reports the 75th percentile (p75) of each metric: the value that 75% of visits were at or better than. Each metric is rated against Google’s Core Web Vitals thresholds:
| Check | Good | Needs attention | Poor |
|---|---|---|---|
| Real-user LCP | 2.5 s or less | over 2.5 s, up to 4 s | over 4 s |
| Real-user CLS | 0.1 or less | over 0.1, up to 0.25 | over 0.25 |
We use Google’s own rating for each metric and show the p75 value next to it.
When there is no field data
Many sites show “no field data”. That is not an error. CrUX only publishes data for pages and origins with enough eligible traffic from Chrome users over the last 28 days; Google does not publish the exact cut-off. Small, new or low-traffic sites, and pages behind a login, often do not qualify.
When a single URL lacks enough data, PageSpeed Insights may fall back to data for the whole origin (all pages on the domain combined). In that case the numbers describe the site in general, not this page specifically.
Without field data, rely on the lab metrics. They are a good guide to what real visitors on slower phones experience.
Why field and lab results differ
- Different devices and networks. The lab emulates one mid-range phone on a throttled connection. Your real audience may use faster or slower devices.
- Different moments. Lab LCP and CLS cover the initial load only. Field CLS keeps counting while people scroll and use the page, so shifts caused by lazy-loaded content, infinite scroll or late ads appear only in field data.
- Caching and repeat visits. Returning visitors often load from cache; the lab test is a cold load.
- Time window. Field data is a 28-day rolling window. A fix you deployed today takes up to four weeks to be fully reflected.
How to improve field results
- Fix the lab metric first. Improvements to lab LCP and CLS usually carry over. Follow the LCP and CLS guides.
- Look beyond the initial load for CLS. Scroll through the page on a phone and watch for content that jumps: ads, embeds, lazy-loaded images without dimensions, and “load more” sections.
- Check your slowest audiences. If many visitors use low-end phones or slow mobile networks, p75 is set by them. Lighter pages help most there.
- Measure your own real users. The open-source
web-vitalsJavaScript library reports LCP, INP and CLS from your visitors to your analytics, with details about which element or interaction caused a poor value. That gives you feedback in days instead of waiting for the 28-day window. - Be patient. After a fix, expect field values to improve gradually over the following weeks.