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Google PageSpeed Insights vs. Lighthouse: Which Measures Site Performance Best?

Concerned about how quickly your web pages are loading? Not sure how to best measure page speed? Read on to learn more about two important page speed tools: Google PageSpeed Insights and Google Lighthouse. I’ll share how they gather data, what you’ll learn from each, and which tool you should use to monitor your site’s page speed.

May 20, 2024

5 m read

Page speed is an important Google ranking factor — but it’s also one of the most poorly understood by digital marketers. In this article, I’ll help you better understand page speed and compare Google’s official tracking tools: PageSpeed Insights and Lighthouse.

What Is Page Speed?

Page speed is the amount of time between when a browser sends a request to access a page and when the page renders the content. Pages are composed of many visible and invisible components (images, text, trackers, plugins, etc.) with varying load times and user purposes. Google breaks down page speed into specific metrics that measure loading milestones, such as first contentful paint and time to interactive. 

Page speeds fluctuate as your site grows, technology changes, and web standards evolve. It can impact how visitors use your site and even whether they convert. Thus, tracking page speeds should be a fundamental part of your regular site health monitoring process.

But what’s the best page speed tracking tool? 

Google offers two official options: Google PageSpeed Insights and Lighthouse. Both are free, powerful tools designed to help digital marketers and developers optimize their website page speed — with a few key differences between them. Let’s compare PageSpeed Insights vs. Lighthouse and discuss what you need to know about tracking and improving page speed.

What Is Google PageSpeed Insights?

Google PageSpeed Insights (PSI) is a free tool that measures page speed metrics on desktop and mobile devices using both real-world and lab data. Real-world data (also called “field data”) is a 28-day aggregate pulled from the Chrome User Experience Report, while lab data is calculated using the Lighthouse API.

PSI is simple for anyone to use: just head to, plug in a URL, and wait a few moments for the API to generate a report. You’ll be able to see how the URL stacks up against Google’s Core Web Vitals, assess detailed speed metrics, and receive an overall website Performance Score.

The Performance Score is a weighted average of each speed metric score. It’s like an overall grade but isn’t an end-all-be-all measurement. The percentages in parentheses below indicate the weight each metric is given when calculating it.

  • First Contentful Paint: (10%) How long it takes for the first image or text block to load fully.
  • Speed Index: (10%) The average time it takes for visible content to load until the screen is complete.
  • Largest Contentful Paint: (25%) How long it takes for the largest image or text block to load fully.
  • Time to Interactive: (10%) How long it takes for a page to become fully interactive.
  • Total Blocking Time: (30%) The time difference between First Contentful Paint and Time to Interactive during which a page is blocked from user input. (In other words, the time difference between when something first appears on-screen vs. when the user can actually click on it.)
  • Cumulative Layout Shift: (15%) A measure of unexpected layout shifts, i.e., content loading out-of-order that reorganizes or shifts other content up or down the page. 

Don’t be too concerned if your website’s Performance Rating isn’t perfect or if some of your metrics seem low. Speed metrics can fluctuate depending on a few factors outside your control. Remember that these metrics are an aggregate of data and actual experiences will vary from user to user. 

That said, you can maximize your Performance Rating and improve page speed by focusing on the ‘Opportunities and Diagnostics’ sections near the bottom of the report. These sections contain recommendations for specific actions that can improve speed metrics, though they may require help from an SEO web developer to implement.

What Is Google Lighthouse?

Google Lighthouse is a free, open-source tool that can perform site audits to measure many different metrics. In addition to assessing page speed, Lighthouse can evaluate how well a site fits modern web development standards, a site’s level of accessibility, crawlability, and more.

Lighthouse exclusively uses lab data, which means audits are run in a controlled, pre-defined environment — not gathered from actual user data.

There are a few different ways to access the Google Lighthouse speed test. The easiest way for non-developers to use Lighthouse is through the Chrome browser extension, though the extension cannot audit pages with cookie authentication on its own. Developers can use Chrome DevTools for complete access.

Your Lighthouse report will include information about:

  • Performance: Performance audits measure all of the same speed metrics as PSI, plus provide more detailed development data.
  • Best Practices: Best Practices audits look at a site’s overall “code health” compared to modern development standards, including security standards.
  • Accessibility: It’s impossible to distill web accessibility into a single score, so Accessibility audits look for various opportunities for improvement in design, user interfaces, language, development, and other areas.
  • SEO: Search engine optimization (SEO) audits provide a basic test for checking if search engines can easily crawl your page. 
  • Progressive Web App: If your site is a Progressive Web App, this audit measures its general speed, reliability, and installability.

What Are Lighthouse Stack Packs?

Stack Packs are one of Lighthouse’s most recent features. With Stack Packs, developers can view stack-based recommendations depending on which stacks a page uses. These recommendations are more relevant than the standard general recommendations offered by Lighthouse, which aren’t compatible with every tool and platform. New Stack Packs are frequently released, so visit the official Github repository to learn more.

Google PageSpeed Insights vs. Lighthouse

Google PageSpeed Insights combines lab and field data to provide a thorough, easy-to-understand overview of a page’s speed. Lighthouse is developer-focused and collects lab data from audits that cover everything from page load speed and web security to accessibility and best practices. Both offer improvement recommendations.

Google PageSpeed Insights vs. Lighthouse: Overview

FeatureGoogle PageSpeed InsightsGoogle Lighthouse
How to Access (browser access; no log-in needed) Google Chrome browser extension (recommended for non-developers)
Chrome DevTools
Node CLI tool
Lighthouse CI (Github link)
Data SourcingChrome User Experience Report (field data)
Lighthouse API (simulated lab data)
Lighthouse API
AssessesmentOne page at a timeOne page at a time or multiple pages at once
MetricsCore Web Vitals, page speed performance metrics (First Contentful Paint, Speed Index, Largest Contentful Paint, Time to Interactive, Total Blocking Time, Cumulative Layout Shift)Performance (including page speed metrics), Accessibility, Best Practices, SEO, Progressive Web App (if applicable)
RecommendationsSection labeled ‘Opportunities and Diagnostics’ that provides specific recommendations for increasing page speed. Section labeled ‘Opportunities and Diagnostics’ provides specific recommendations for increasing page speed. Stack Packs can be used to tailor improvement recommendations.
Best ForEveryoneDevelopers

When To Use Google PageSpeed Insights

Use PSI if you want a clear understanding of a URL’s speed and specific improvement recommendations to implement yourself or relay to a developer.

When To Use Google Lighthouse

Use Lighthouse if you’re a developer (or non-developer with some dev knowledge) and want a deep dive into many different site metrics beyond page speed. Stack Packs can help provide more tailored recommendations than the standard ones offered by Lighthouse.

Want the Best Data? Use Both PageSpeed Insights & Lighthouse

PSI and Lighthouse each have their strengths and limitations — but they’re most effective when used together to build a complete picture of your site. In fact, a reputable SEO agency would probably use both.

While Lighthouse provides a broader view of data, PageSpeed Insights gives you a more realistic glimpse at how web pages perform for actual users. Use both to get recommendations for improving your site’s front- and back-ends. The more data you have at your disposal, the more effective your site adjustments will be.

Make the Most of Google Tools With Our Free Resources

If you take away one thing from this article, it should be that page speed is important — and much more complex than it seems on the surface. Just like there’s not just one way to boost a site’s speed, there isn’t only one way to boost your site’s search engine performance — or even one best Google tool to track data.

Optimizing your site involves juggling a lot of data and navigating complicated tools. To make things less complicated, check out our other Google tools resources.

Want help improving your performance in search? Sign up for a free SEO consultation.

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