Website speed test
Paste a URL. We run Google Lighthouse on a throttled phone and a desktop at the same time, pull 28 days of real-user Chrome data, and show you frame by frame how your page loads and what to fix first.
Runs Google Lighthouse on mobile and desktop at the same time, plus real-user Chrome data. Takes about 20–40 seconds.
Two kinds of numbers, and which one Google uses
A speed report mixes two very different measurements. Lab data is one page load that Lighthouse runs on Google’s servers under fixed, deliberately slow conditions. It is repeatable and full of diagnostics, which makes it the right tool for finding problems. Field data comes from the Chrome UX Report: timings collected from real Chrome users who visited your page over the last 28 days, on whatever phones and networks they actually had.
Google’s ranking systems look at the field data, and specifically at the 75th percentile: the visit that is slower than three quarters of all visits. That means your fastest visitors don’t decide your result. Your slow ones do. Drag the sliders below to see why a site that feels fast on your office Wi-Fi can still fail.
Why the 75th percentile catches slow visitors
Median visit: 1.91 s. 75th-percentile visit (the one Google reports): 4.75 s → Poor
Each bar is one visit, sorted from fastest to slowest. The outlined bar is visit 75. Push the slow share past 25% and the p75 lands in the slow group, however fast your typical visit is.
The same idea explains most “it’s fast for me” arguments: the person saying it is usually on a fast laptop, close to the server, with a warm cache. When you want the intuition instead of the assertion, ahaboo lets you experiment with the underlying model and see the numbers respond as you change things.
Why mobile scores lower than desktop
Lighthouse’s mobile profile emulates a mid-range Android phone on a slow 4G connection, and it slows the CPU down four times. Desktop gets a fast connection and full CPU speed. Heavy JavaScript is punished twice on mobile: it takes longer to download and longer to run.
Same page, two devices
Mobile: 150 ms round trips, 1.6 Mbps, CPU slowed 4×
≈ LCP 5.59 s Poor
Desktop: 40 ms round trips, 10 Mbps, full-speed CPU
≈ LCP 1.1 s Good
A deliberately simple model (it ignores caching, HTTP/2 multiplexing and image loading) that uses Lighthouse’s published throttling settings. The point: JavaScript costs you twice on mobile, once to download over a slow link and again to run on a slow CPU.
What the speed test measures
| Metric | What it tells you | Good | Used by |
|---|---|---|---|
| Largest Contentful Paint | When the main content (usually the hero image or headline) is visible | ≤ 2.5 s | Core Web Vital · Lighthouse 25% |
| Interaction to Next Paint | How quickly the page responds to taps, clicks and typing | ≤ 200 ms | Core Web Vital (field only) |
| Cumulative Layout Shift | How much content jumps around while loading | ≤ 0.1 | Core Web Vital · Lighthouse 25% |
| Total Blocking Time | How long JavaScript blocks the main thread (lab stand-in for INP) | ≤ 200 ms | Lighthouse 30% |
| First Contentful Paint | When anything at all appears | ≤ 1.8 s | Lighthouse 10% |
| Speed Index | How quickly the visible page fills in overall | ≤ 3.4 s | Lighthouse 10% |
| Time to First Byte | How long the server takes to start sending the page | ≤ 0.8 s | Diagnostic |
Mobile thresholds shown. The Lighthouse weights come from Lighthouse 10 and later; see the score calculator for how they combine.
Other ways to look at the same page
- Core Web Vitals checkerPass or fail on LCP, INP and CLS from real users, first.
- Lighthouse testAll four Lighthouse categories with every failed audit.
- Website graderA–F grades for speed, accessibility, best practices and SEO.
- TTFB checkerDNS, connect, TLS and server time, split out.
- Speed optimization checklistThe fixes that move each metric, in order.
Questions people ask
Is this website speed test free?
Yes. There is no sign-up and no limit from us. Tests run through Google’s public PageSpeed Insights API, which has a shared daily quota; if it is ever exhausted you can paste your own free API key and keep testing.
Why is my mobile score so much lower than desktop?
Lighthouse tests “mobile” on a simulated mid-range phone: slow 4G (150 ms round trips, about 1.6 Mbps) and a CPU slowed down four times. The same page therefore takes several times longer to download and run its JavaScript. Most real visitors are on phones, so the mobile number is the one to work on.
Why does my score change every time I test?
Each lab test is a single page load, and server response time, third-party scripts, ads and network routes vary between runs. Swings of 5–10 points are normal. Compare runs over time, and rely on the real-user (field) data for decisions.
Does the performance score affect my Google rankings?
Not directly. Google’s page experience signals use the Core Web Vitals from real Chrome users (LCP, INP and CLS at the 75th percentile), shown in the “What real visitors experience” section. The Lighthouse score is a lab diagnostic that helps you find what to fix.
What counts as a good website loading speed?
Google’s thresholds: the largest element should appear within 2.5 seconds (LCP), the page should respond to taps within 200 ms (INP), and layout should barely move (CLS of 0.1 or less), for at least 75% of visits. A Lighthouse performance score of 90+ is “good”.
Can I test pages behind a login or on localhost?
No. Google’s servers load the page, so it must be publicly reachable. For staging or local pages, run Lighthouse from Chrome DevTools (Lighthouse panel) on your own machine.