Lighthouse performance scoring
How Lighthouse calculates your overall Performance score
In general, only metrics audits contribute to your Lighthouse Performance score.
For each metrics audit, your page is assigned a score from 0 to 100 based on real website performance data from the HTTP Archive. 0 is the lowest possible score and usually indicates an error in Lighthouse. 100 is the highest possible score and indicates your page is in the ninety-eighth percentile of websites for that metric.
Why your score fluctuates
A lot of the variability in your overall Performance score and metric scores is not due to Lighthouse. Project Lantern has minimized much of the variance in Lighthouse's measurements.
When your Performance score fluctuates it's usually because of changes in underlying conditions. Common problems include:
- A/B tests
- Internet traffic routing changes
- Testing with different versions of Lighthouse
- Testing on different devices, such as a high-performance desktop and a low-performance laptop
- Browser extensions that inject JavaScript into all pages you visit and make network requests
Furthermore, even though Lighthouse can provide you a single overall Performance score, it might be more useful to think of your site performance as a distribution of scores, rather than a single number. See the introduction of User-Centric Performance Metrics to understand why.
How the performance metrics are weighted
Each audit is weighted based on heuristics. More heavily weighted audits have a bigger effect on your overall Performance score. The tables below show the weighting for each metric in each version of Lighthouse.
The weightings have changed over time because the Lighthouse team is regularly doing research and gathering feedback to understand which metrics have the biggest impact on user-perceived performance.
Lighthouse 6 (draft)
| Audit | Weight |
|---|---|
| First Contentful Paint | 15% |
| Speed Index | 15% |
| Largest Contentful Paint | 25% |
| Time to Interactive | 15% |
| Total Blocking Time | 25% |
Lighthouse 5
| Audit | Weight |
|---|---|
| First Contentful Paint | 20% |
| Speed Index | 27% |
| First Meaningful Paint | 7% |
| Time to Interactive | 33% |
| First CPU Idle | 13% |
Historical versions
Lighthouse 3 and 4
| Audit | Weight |
|---|---|
| First Contentful Paint | 23% |
| Speed Index | 27% |
| First Meaningful Paint | 7% |
| Time to Interactive | 33% |
| First CPU Idle | 13% |
Lighthouse 2
| Audit | Weight |
|---|---|
| First Contentful Paint | 6% |
| Speed Index | 6% |
| First Meaningful Paint | 29% |
| Time to Interactive | 29% |
| First CPU Idle | 29% |