# Lighthouse scoring and audits — Web Performance Optimization

Source: https://www.skillbyai.com/en/web-performance/web-perf-17

> Understand Lighthouse scoring methodology and use audit results to prioritize optimizations.

## Performance score calculation

The Lighthouse performance score is a weighted blend of lab metrics: Total Blocking Time (30%), LCP (25%), CLS (25%), FCP (10%) and Speed Index (10%). Scores of 90–100 are good, 50–89 need improvement, and below 50 is poor. Weights change between Lighthouse versions, so check the current calculator.

## Audit opportunities and diagnostics

Lighthouse lists specific issues: unoptimized images, unused JavaScript, slow server response, missing cache headers. Prioritize high-impact suggestions. Diagnostic metrics show underlying bottlenecks like unused CSS or render-blocking resources.

## Interpreting Lighthouse results

Focus on opportunities section, not just score. Test multiple times—results vary. Throttling affects measurements. Compare baseline vs. improved. Set incremental goals (e.g., 50 → 70 → 90).

Quick check

**Quiz:** What is the weight of LCP in Lighthouse scoring?

- [ ] 15%
- [x] 25%
- [ ] 10%
- [ ] 50%

*Answer:* 25%. LCP carries a 25% weight in the current Lighthouse performance score.