PageSpeed Insights is Google's free tool for measuring how quickly a web page loads and how stable it is while loading. You type in an address and get a score from 0 to 100 for mobile and for desktop. A higher score usually means visitors see your content sooner and can use the page without waiting. This guide explains what the score measures, how to read it, and what to do about a low one.

What the score measures

The performance score comes from Lighthouse, a testing tool built into Chrome. PageSpeed Insights loads your page on a simulated mid-range phone over a slow mobile connection (or on a desktop, for the desktop tab) and times what happens. The score combines five measurements:

  • First Contentful Paint: when the first text or image appears.
  • Largest Contentful Paint: when the biggest piece of content, usually a headline or hero image, appears. This is the one most people feel as “the page loaded”.
  • Total Blocking Time: how long the browser is too busy running code to respond to a tap or click.
  • Cumulative Layout Shift: how much the page jumps around as it loads, for example when an image pushes text down just as you try to tap a button.
  • Speed Index: how quickly the visible part of the page fills in overall.

How to read the score

PageSpeed Insights colours the score in three bands:

  • 90 to 100 (green): good.
  • 50 to 89 (orange): needs improvement.
  • 0 to 49 (red): poor.

Look at the mobile score first. Most sites score lower on mobile because the test simulates a slower device and connection, and many of your visitors arrive on a phone.

Lab data and real-visitor data

The score is lab data: one simulated visit under fixed conditions. If your site gets enough traffic from Chrome users, PageSpeed Insights also shows field data from real visitors over the previous 28 days, labelled “Discover what your real users are experiencing”. Smaller sites often see “No data” there, which is normal.

Field data is where Google's Core Web Vitals come from. Google describes a page as good when its main content appears within 2.5 seconds, it responds to interactions within 200 milliseconds, and its layout shift stays below 0.1. Google says this kind of page experience aligns with what its ranking systems reward, alongside many other signals.

Why it matters to a business

A slow page costs you in two ways. Some visitors leave before it finishes loading, and the ones who stay have a worse experience on the way to calling, booking or buying. In a study commissioned by Google and run by 55 and Deloitte across 37 brands, a 0.1 second improvement in mobile site speed increased conversion rates by 8.4% for retail sites and 10.1% for travel sites.

The usual causes of a low score

  • Images much larger than the space they are shown in, or in older formats.
  • Page builders, plugins and apps that each add their own code to every page.
  • Tracking, chat and advertising scripts that load before your content.
  • Pages assembled in the visitor's browser instead of arriving ready to display.
  • Slow hosting, or a server that has to build every page from scratch on each visit.
  • Web fonts and late-loading elements that make the layout jump.

What you can do about it

Some fixes are within reach for any site owner:

  • Compress and resize images before uploading them.
  • Remove plugins, apps and scripts you no longer use.
  • Ask your host whether caching is switched on.
  • Re-test after each change so you know what helped.

If the score stays low after the easy fixes, the limit is usually the platform itself: a theme, page builder or plugin stack that loads more than any page needs. That is when rebuilding the slowest parts, or the whole site, starts to pay for itself.