Andrei & Claudiu

How we measure

1. Two kinds of data

  • Real visitors (Chrome UX Report, CrUX): the experiences of real Chrome users who opted in to share usage statistics.
  • Simulated test (Lighthouse, via PageSpeed Insights): one automated load in a controlled environment.

In the report, every value carries a label saying which of the two it comes from.

2. Period

Real-visitor data is a rolling total over the last 28 days. That's why an improvement shows up gradually, not overnight.

3. The 75th percentile

The value shown means at least 75% of page loads were at or below it.

4. Who is counted

Chrome on desktop (Windows, macOS, ChromeOS, Linux) and on Android. Not counted: Chrome on iOS, in-app browsers (Android WebView) and other browsers such as Edge, Safari or Firefox.

5. Why some sites have no real data

A site must be publicly indexable and have enough visitors. Google doesn't publish the threshold. Without real data, we only show the simulated test, and we label it as such.

6. The metrics

  • LCP (Largest Contentful Paint): how long until the largest visible element of the page appears.
  • INP (Interaction to Next Paint): how quickly the page responds after a click or tap.
  • CLS (Cumulative Layout Shift): how much the page's elements jump around while it loads.
  • FCP (First Contentful Paint): how long until the first thing appears on screen.
  • TTFB (Time to First Byte): how long the server takes to respond.

The first three are the Core Web Vitals.

7. Independence

We use public data from Google. We are not affiliated with, sponsored or endorsed by Google.

8. Data source

Real-visitor data: Chrome UX Report (CrUX) by Google, licensed under CC BY 4.0. Values summarised and explained in plain language by AC WEB STUDIO S.R.L.. Simulated test: Google PageSpeed Insights (Lighthouse).