What are the Lighthouse performance score weights?

In Lighthouse 10 and 11 the Performance score is a weighted blend of five lab metrics: Total Blocking Time at 30 percent, Largest Contentful Paint and Cumulative Layout Shift at 25 percent each, and First Contentful Paint and Speed Index at 10 percent each. They sum to 100 percent.

Why is Total Blocking Time weighted so heavily?

TBT is weighted at 30 percent because it is the lab proxy for responsiveness. Lighthouse runs in a lab environment where it cannot measure real interactions, so it uses main-thread blocking time between First Contentful Paint and Time to Interactive as a stand-in for the field INP metric.

Does Lighthouse still score PWA?

No. PWA was removed as a scored category in Lighthouse 12. The installability and offline-related PWA audits still run but are reported as informational checks rather than contributing to a 0-100 score. The four scored categories are Performance, Accessibility, Best Practices and SEO.

Can Lighthouse catch every accessibility issue?

No. Automated tools like Lighthouse can detect roughly a third of accessibility problems — things like color contrast, missing labels and invalid ARIA. The remaining issues, such as logical focus order and meaningful alt text, require manual testing with a keyboard and screen reader.

How are the category scores banded?

Each category score is graded as Good for 90 to 100, Needs Improvement for 50 to 89, and Poor for 0 to 49. The colored gauge in a Lighthouse report (green, orange, red) reflects these same three bands.

What is the Lighthouse Audit Categories Reference?

Searchable Lighthouse reference covering the Performance, Accessibility, Best Practices, SEO and PWA categories, the metric audit IDs, and the exact scoring weights (LCP 25%, TBT 30%, CLS 25%) that build the Performance score. It runs free in your browser on Gera Tools, with nothing uploaded.

Lighthouse Audit Categories Reference

Name: Lighthouse Audit Categories Reference
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Lighthouse runs a battery of automated audits and rolls them up into category scores, but the headline number hides how it is calculated. Understanding which audits belong to which category — and how much each weighs — is the difference between guessing and fixing the right thing. This reference lists every category, the key audit IDs, and the precise weights that build the Performance score.

The five Lighthouse categories

Category	Scored?	Notes
Performance	Yes (0–100)	Weighted blend of five lab metrics
Accessibility	Yes (0–100)	Axe-based automated checks
Best Practices	Yes (0–100)	Security, modern APIs, safe practices
SEO	Yes (0–100)	Crawlability, meta, links, structured data
PWA	No (informational)	Demoted from scored in Lighthouse 12

Performance score weights

In Lighthouse 10 and 11 the Performance score is a weighted average of five lab metrics:

Metric	Audit ID	Weight
Total Blocking Time	total-blocking-time	30%
Largest Contentful Paint	largest-contentful-paint	25%
Cumulative Layout Shift	cumulative-layout-shift	25%
First Contentful Paint	first-contentful-paint	10%
Speed Index	speed-index	10%

Each metric is first converted to a 0–1 score using a log-normal curve calibrated against real-world data, then multiplied by its weight and summed. The curves differ between mobile and desktop configurations, which is why the same page can score differently on each preset.

TBT carries the heaviest weight (30%) because it is the best lab proxy for the field INP (Interaction to Next Paint) responsiveness metric. Lighthouse cannot measure real user interactions in a lab environment, so it uses the total time the main thread is blocked between First Contentful Paint and Time to Interactive as its stand-in.

Score bands

Score	Band	Gauge colour
90–100	Good	Green
50–89	Needs Improvement	Orange
0–49	Poor	Red

These same bands apply to all four scored categories.

What automated audits cannot catch

The Accessibility and SEO categories are particularly susceptible to false confidence. A score of 100 means automated checks passed — it does not mean the experience is accessible or discoverable. Rough guidance:

Accessibility: automated tools catch roughly 30–40% of issues. Colour contrast, missing labels and invalid ARIA are detectable; logical focus order, meaningful alt text, and screen-reader announcement order require manual testing.
SEO: Lighthouse checks technical signals (canonical, meta description, crawlable links) but cannot evaluate content quality, topical authority or off-page signals.

When optimizing Performance, attack the heavily weighted metrics first. Shaving TBT (30%) and LCP (25%) moves the headline score dramatically more than tuning Speed Index (10%).