What the numbers mean
A quick guide for website owners. No technical knowledge needed.
The performance score (0-100)
Google Lighthouse loads your page in a lab and turns five timings into one score. 90 or more is good, 50 to 89 needs improvement and below 50 is poor. Mobile scores are usually lower because the test simulates a mid-range phone on a slow 4G connection.
Core Web Vitals
Three measurements Google uses to judge the experience of real visitors, and a factor in search ranking. They come from people using Chrome on your site over the last 28 days.
| Metric | Good | Needs improvement | Poor |
|---|---|---|---|
| LCP When the main content (the biggest image or text block) is shown. Good: 2.5 s or less. | ≤ 2.5 s | 2.5 - 4 s | > 4 s |
| INP How quickly the page reacts to taps, clicks and typing. Good: 200 ms or less. | ≤ 200 ms | 200 - 500 ms | > 500 ms |
| CLS How much the content jumps around while loading. Good: 0.1 or less. | ≤ 0.1 | 0.1 - 0.25 | > 0.25 |
Lab data or real visitors?
Real-visitor data shows what people really experienced, but it only exists for sites with enough traffic. The lab test runs on demand for any public page and is what you use to find and check fixes.
- FCP · First Contentful Paint
- When the first text or image appears.
- LCP · Largest Contentful Paint
- When the main content (the biggest image or text block) is shown. Good: 2.5 s or less.
- TBT · Total Blocking Time
- How long the page is frozen by scripts while loading, so taps and clicks do nothing.
- CLS · Cumulative Layout Shift
- How much the content jumps around while loading. Good: 0.1 or less.
- SI · Speed Index
- How quickly the visible part of the page fills in.
- INP · Interaction to Next Paint
- How quickly the page reacts to taps, clicks and typing. Good: 200 ms or less.
- TTFB · Time to First Byte
- How long the server takes to start sending the page.
How to use the recommendations
Start with the three items marked "Fix first": they save the most time. Send the share link to your developer - every item has a "Technical details" section with the exact files and sizes.
Common questions
Why does my score change between tests?
Network conditions, ads, and server load change from run to run. Differences of a few points are normal. Look at trends, not single runs.
Why is my mobile score much lower than desktop?
The mobile test simulates a slower phone and connection, which is how many real visitors browse. Improve mobile first.
Can I test a page that needs a login?
No. The page must be reachable by anyone on the internet without a password.