To check a page’s speed in Google Chrome, use Lighthouse, which is built into Chrome DevTools. Open the page, press F12 (or Command + Option + I on a Mac), click the Lighthouse tab, and click Analyze page load. For Google’s online version, go to PageSpeed Insights at pagespeed.web.dev and paste in the URL.
This guide covers running Lighthouse in Chrome, using PageSpeed Insights, reading the scores, and getting more consistent results. It is based on Google’s Introduction to Lighthouse, Lighthouse: Optimize your website, Open Chrome DevTools and About PageSpeed Insights.
What Lighthouse Checks
Google describes Lighthouse as a free, open-source tool that audits a web page and produces a report. You can run it on any page, including pages that need you to sign in. The DevTools report scores four categories:
- Performance
- Accessibility
- Best Practices
- SEO
Each category gets a score, along with issues and suggestions. Google says each audit links to an explanation of why it matters and how to fix it.
How to Run a PageSpeed Test in Chrome (Lighthouse)
- Open the web page in Chrome on a computer.
- Open DevTools. Press F12 or Ctrl + Shift + I on Windows, or Command + Option + I on a Mac. You can also click the three-dot menu and choose More Tools > Developer Tools.
- Click the Lighthouse tab.
- Choose Mobile or Desktop, and check the categories you want.
- Click Analyze page load.
Result: Google says Lighthouse produces its report after 30 to 60 seconds. Picking fewer categories can make the audit faster, according to Google’s DevTools documentation.
Lighthouse modes and settings
Google says the default Navigation mode tests a fresh page load. Timespan mode records while you interact with the page, and Snapshot mode audits the page in its current state without reloading. The settings (gear) button adds options such as Clear storage and a throttling choice.
After the run, Google says the three-dot menu lets you print, copy or save the report, open it in a separate viewer, or view the trace in the Performance panel.
How to Use PageSpeed Insights
- Go to pagespeed.web.dev.
- Paste the page URL and click Analyze.
- Review the mobile and desktop results.
Result: Google says PageSpeed Insights shows two kinds of data. Field data comes from real Chrome users through the Chrome UX Report, covering the previous 28 days, and includes the Core Web Vitals (LCP, INP and CLS). Lab data comes from running Lighthouse in a simulated environment. If a page doesn’t have enough real-user data, PSI falls back to data for the whole site, or shows none. PageSpeed Insights picks the test location closest to you.
How to Read the Scores
Google’s PageSpeed Insights documentation says a category score of 90 or above is good, 50 to 89 needs improvement, and below 50 is poor. For field data, Google lists these “good” thresholds:
- Largest Contentful Paint (LCP): 2.5 seconds or less
- Interaction to Next Paint (INP): 200 ms or less
- Cumulative Layout Shift (CLS): 0.1 or less
Google says a page passes the Core Web Vitals assessment when the 75th percentile of all three metrics is good.
How to Get More Consistent Results
Google warns that Lighthouse in DevTools is affected by your setup, including other load on your computer, Chrome extensions, and data stored in cookies or local storage. Running it in an Incognito window is often recommended, but Google notes that even that may not remove every influence, and you can’t directly compare audits from different computers. PageSpeed Insights runs on Google’s servers, so Google says it can give cleaner, more consistent results that are easier to compare.
Which Should You Use?
- PageSpeed Insights: a quick check of any public page, plus real-user data when available.
- Lighthouse in DevTools: tests pages that need a sign-in, and lets you pick the device and categories.
- Performance panel: for deeper debugging, Google now recommends the DevTools Performance panel over Lighthouse.
Frequently Asked Questions
Is Lighthouse free?
Yes. Google describes Lighthouse as an open-source tool. It is built into Chrome DevTools, and you can also run it from the command line or through PageSpeed Insights.
Why do my Lighthouse and PageSpeed Insights scores differ?
Lighthouse in DevTools runs on your own computer, so Google says your hardware, extensions and stored data can affect the result. PageSpeed Insights runs Lighthouse on Google’s servers and also adds real-user field data.
Related Guides
- How to use the Chrome Task Manager
- How to turn off hardware acceleration in Chrome
- How to upload files to a web server with FileZilla
Matthew Burleigh is the founder, head writer, and editor of Solve Your Tech, which he launched in 2012. He has written technology tutorials since 2008 and worked in IT since 2003, including small-business support, IT management, and consulting. He holds Bachelor’s and Master’s degrees in Computer Science from Arizona State University.
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