Enter the five metric values from your Lighthouse report and see the sub-score each one earns, what it contributes to the total, and how many points are still available on it. The arithmetic is the one Lighthouse uses.
| Metric | Sub-score | Weight | Points | To gain |
|---|---|---|---|---|
| TBT Total Blocking Time | 90 | 30% | 27.0 / 30 | - |
| LCP Largest Contentful Paint | 90 | 25% | 22.5 / 25 | - |
| CLS Cumulative Layout Shift | 90 | 25% | 22.5 / 25 | - |
| FCP First Contentful Paint | 90 | 10% | 9.0 / 10 | - |
| SI Speed Index | 90 | 10% | 9.0 / 10 | - |
Every metric is already at or past its 0.9 control point. Further gains are small and come from the tail of the curve.
Each metric becomes a sub-score through a log-normal curve defined by two control points: the value scoring 0.9 and the value scoring 0.5. Because the curve is continuous, there is no cliff at the good threshold. Going from 4.0 s to 3.5 s of LCP earns real points even though both sit outside the good range, while shaving 100 ms off an already fast metric earns almost nothing.
The five sub-scores are then combined with fixed weights. Total Blocking Time alone carries 30 percent, which is why a page with excellent paint timings can still score badly if the main thread is busy.
| Metric | Weight | Mobile | Desktop |
|---|---|---|---|
| TBT | 30% | 200ms / 600ms | 150ms / 350ms |
| LCP | 25% | 2500ms / 4000ms | 1200ms / 2400ms |
| CLS | 25% | 0.1 / 0.25 | 0.1 / 0.25 |
| FCP | 10% | 1800ms / 3000ms | 934ms / 1600ms |
| SI | 10% | 3387ms / 5800ms | 1311ms / 2300ms |
Curve and control points read from the Lighthouse source. This tool computes the score from values you enter; it does not measure your site, and field data from real users can differ from any lab run. Independent tool, not affiliated with Google.
Related tool: Core Web Vitals checker - Total Blocking Time