Crux
The score on the slide is not the score in the wild.
Lighthouse runs a simulated single load on a throttled emulated device. CrUX tracks real Chrome users over the previous 28 days. The PSI score everyone quotes is the lab score.
Lab vs field
Lighthouse is a controlled lab test. CrUX is field data collected from real users. PSI shows both, but the number people talk about in meetings is the lab score, not the field picture.
How the score is weighted
| Metric | Weight |
|---|---|
| Total Blocking Time | 30% |
| Largest Contentful Paint | 25% |
| Cumulative Layout Shift | 25% |
| First Contentful Paint | 10% |
| Speed Index | 10% |
Why these demo pages show no field data
CrUX needs enough real traffic volume before it can report a page or origin. When PSI shows no field data here, that is the point: the missing field panel proves the page score clients see is not measuring their actual users yet.
Nobody scores 100
- Amazon
- Walmart
- Nike
- ASOS
- SHEIN
- Gymshark
- Fashion Nova
- Allbirds
- Kylie Cosmetics
- Sephora
What actually matters
The goal is passing Core Web Vitals in field data: Largest Contentful Paint at or below 2.5 seconds, Interaction to Next Paint at or below 200 milliseconds, and Cumulative Layout Shift at or below 0.1.