What Is a Lighthouse Score?
A Lighthouse score is a 0-to-100 rating from Google's open-source Lighthouse tool that audits a web page across five categories: Performance, Accessibility, Best Practices, SEO, and Progressive Web App readiness. Performance is the most cited score, calculated from lab metrics like Largest Contentful Paint and Total Blocking Time. Scores are diagnostic, run in a controlled environment, so they guide improvements but do not directly determine Google rankings the way real-user field data does.
- Score range
- 0 to 100 per category; 90+ is good, 50-89 needs work (Google)
- Five categories
- Performance, Accessibility, Best Practices, SEO, PWA (Google)
- Data type
- Lab data from a simulated load, not real-user field data (Google)
- Built into
- Chrome DevTools, PageSpeed Insights, and the CLI (Google)
What is Lighthouse and what does it score? #
Lighthouse is a free, open-source auditing tool built by Google that analyzes any web page and grades it across five categories, each scored from 0 to 100. The categories are Performance, which measures loading speed and responsiveness; Accessibility, which checks how usable the page is for people with disabilities; Best Practices, which covers modern web standards and security; SEO, which flags basic search-optimization issues; and Progressive Web App, which assesses app-like capabilities. Lighthouse runs a simulated page load in a controlled environment, applying a throttled network and CPU to mimic a mid-range mobile device, then reports scores plus detailed diagnostics and specific recommendations. It is built into Chrome's DevTools, powers the lab section of Google's PageSpeed Insights, and can run from the command line for automated testing. The Performance score is the most talked about, but all five categories offer useful guidance. For a local business, Lighthouse is a practical health check that turns vague notions of a slow or clunky site into concrete, prioritized fixes. Our /tools/website-grader draws on the same underlying signals, and we act on them in /services/speed-optimization.
How is the Performance score calculated? #
The Lighthouse Performance score is a weighted average of several lab metrics that together approximate how fast a page loads and becomes usable. The current metrics include Largest Contentful Paint, when the biggest visible element renders; Total Blocking Time, how long the main thread was blocked and unable to respond, which correlates with interaction responsiveness; Cumulative Layout Shift, how much the layout moves during load; First Contentful Paint, when the first content appears; and Speed Index, how quickly the page visually fills in. Each metric carries a weight, with Total Blocking Time and Largest Contentful Paint weighted heavily in recent versions, and the weighted result maps to the 0-to-100 score. Because these are lab measurements from a single simulated load, the score can vary between runs depending on conditions, so it is best read as a range rather than a precise figure. Understanding which metric is dragging the score down tells you where to focus, whether that is images, scripts, or layout stability. We diagnose the specific weak metric during /services/speed-optimization rather than chasing the headline number blindly. See the metrics in context in /wiki/website-speed-guide.
What is a good Lighthouse score? #
Lighthouse groups scores into three bands shown with color coding. A score of 90 to 100 is good and displayed in green, 50 to 89 needs improvement and appears orange, and 0 to 49 is poor and shown in red. Aiming for 90 or above in each category is a reasonable target, though the practical importance varies. A strong Performance score reflects a genuinely fast page, and the Accessibility, Best Practices, and SEO categories catch real issues worth fixing. That said, chasing a perfect 100 can hit diminishing returns, and some businesses spend disproportionate effort squeezing the last few points that visitors never notice. A more useful goal is a solidly good score with no critical diagnostics outstanding, which usually means the site is fast and well-built. It is also worth remembering that scores fluctuate between runs and that mobile scores are typically lower than desktop because of the throttling Lighthouse applies. For local businesses, we target a good score across categories while prioritizing the fixes that most affect real customers, and we track progress with /tools/website-grader.
Lighthouse lab data versus field data #
The most important thing to understand about Lighthouse is that it produces lab data, not field data, and the distinction matters for SEO. Lab data comes from a single controlled test on Google's simulated device and network, useful for diagnosing problems and confirming fixes because it is repeatable. Field data comes from real Chrome users visiting your site on their own devices and connections, collected in the Chrome User Experience Report and shown in the field section of PageSpeed Insights and in Google Search Console. It is field data, not the Lighthouse lab score, that feeds Google's page experience signals and affects rankings. This is why a page can post a high Lighthouse score yet still fail Core Web Vitals in the real world, or vice versa, because real users face conditions the lab does not replicate. The right way to use Lighthouse is as a fast diagnostic and debugging tool, then confirm improvements in field data over the following weeks. We use both together in /services/speed-optimization, and explain the interaction-focused field metric in /wiki/what-is-interaction-to-next-paint.
Does a Lighthouse score affect Google rankings? #
This is a common misconception. The Lighthouse Performance score itself is not a Google ranking factor. What can influence rankings, modestly, are Core Web Vitals measured from real-user field data, which is separate from the lab-based Lighthouse number. A high Lighthouse score is a good sign your field metrics will be healthy, but it is not a guarantee, and Google does not read your Lighthouse score when ranking pages. Furthermore, Google has consistently said that content relevance and quality far outweigh page experience, so a fast page with weak content will not outrank a slower page that better answers the query. The useful role of the Lighthouse score is diagnostic: it helps you find and fix the issues that will improve real-user metrics and, more importantly, the actual visitor experience that drives conversions. For local businesses, a fast, accessible, well-built site keeps hard-won visitors moving toward booking and contact. We pair Lighthouse-guided speed work with /services/local-seo and /services/conversion-optimization, since usability and content together move the needle.
What do the other Lighthouse categories check? #
Beyond Performance, Lighthouse's four other categories each surface valuable issues. Accessibility checks whether the page works for people using assistive technology: it flags missing image alt text, poor color contrast, unlabeled form fields, and improper heading structure, all of which also affect usability and legal compliance; our /tools/ada-compliance-checker digs deeper here. Best Practices reviews modern standards and security, such as serving over HTTPS, avoiding deprecated code, and correct image aspect ratios. The SEO category runs basic checks like a valid title tag, meta description, crawlability, and mobile friendliness, though it is a starting point rather than a full audit; deeper work happens in /services/local-seo. The Progressive Web App category assesses app-like features such as offline support and installability, which matters mainly for sites pursuing that model. Reading all five categories together gives a rounded health check of a site, not just its speed. We address the full set in /services/web-design and /services/speed-optimization, and use /tools/website-grader to summarize the findings for non-technical owners in plain language.
How do you run a Lighthouse audit? #
Running Lighthouse is simple and free. The easiest way for most people is Google's PageSpeed Insights website: enter a URL and it runs Lighthouse for both mobile and desktop, showing lab scores alongside real-user field data if enough exists. For hands-on debugging, Lighthouse is built into Chrome's DevTools, open the Lighthouse tab, choose categories and device type, and generate a report; this is handy for testing pages behind a login or in development. Developers can also run Lighthouse from the command line to automate audits in a deployment pipeline. When running an audit, test the same page multiple times because scores vary between runs, test on mobile since that is where most local searches happen and scores are stricter, and read the diagnostics and opportunities sections rather than fixating on the number, since those tell you exactly what to fix. After making changes, re-run to confirm the lab improvement, then watch field data over the following weeks. For a plain-English version tailored to local businesses, our /tools/website-grader runs the checks and prioritizes fixes, which we then implement through /services/speed-optimization.
Using Lighthouse scores wisely #
The healthiest way to treat a Lighthouse score is as a compass, not a scoreboard. The number is a useful summary, but the real value is in the diagnostics that tell you which specific issues to fix, oversized images, render-blocking scripts, missing alt text, layout shifts. Focus effort on the changes that meaningfully improve real users' experience, then verify with field data rather than obsessing over lab points. Beware three traps: chasing a perfect 100 at the expense of higher-value work, assuming a good lab score guarantees good field results, and treating the Performance score as a ranking factor it is not. It is also wise to test representative pages, not just the homepage, since templates differ, and to recognize that some low scores come from essential third-party tools where the tradeoff is worth it. For local businesses, the goal is a fast, accessible, credible site that converts visitors, and Lighthouse is one instrument toward that end. We use it alongside field data and business goals in /services/speed-optimization and /services/conversion-optimization, and translate the findings into a clear action plan through /tools/website-grader.
FAQ
What is a Lighthouse score?
A Lighthouse score is a 0-to-100 rating from Google's open-source Lighthouse tool, which audits a web page across five categories: Performance, Accessibility, Best Practices, SEO, and Progressive Web App. It runs a simulated load and reports scores plus specific recommendations. Performance is the most cited, but it is lab data, not a direct ranking factor.
What is a good Lighthouse score?
A score of 90 to 100 is good and shown in green, 50 to 89 needs improvement in orange, and 0 to 49 is poor in red. Aiming for 90 or above per category is reasonable, though chasing a perfect 100 hits diminishing returns. A solid score with no critical diagnostics usually means a fast, well-built site.
Does my Lighthouse score affect Google rankings?
Not directly. The Lighthouse lab score is not a ranking factor. Real-user Core Web Vitals field data can influence rankings modestly, and a high Lighthouse score suggests those will be healthy but does not guarantee it. Google also weighs content relevance and quality far more heavily than page experience signals.
Why is my mobile score lower than desktop?
Lighthouse throttles the network and CPU to simulate a mid-range mobile device, so mobile tests face tougher conditions than desktop. Because most local searches happen on phones, the mobile score is the more important one to improve. Expect mobile numbers to run lower and prioritize fixes accordingly.
What is the difference between lab and field data?
Lab data comes from a single controlled Lighthouse test, ideal for diagnosing and confirming fixes. Field data comes from real Chrome users on their own devices, collected over 28 days. Only field data feeds Google's page experience signals, which is why a high lab score can still coexist with failing real-world metrics.
How do I run a Lighthouse audit?
The easiest way is Google's PageSpeed Insights website: enter a URL for mobile and desktop lab scores plus field data. For debugging, use the Lighthouse tab in Chrome DevTools. Test each page several times since scores vary, focus on mobile, and read the diagnostics rather than fixating on the number.
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