A slow website quietly drains revenue, conversions, and search visibility every single day it runs unoptimised.
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Core Web Vitals: LCP, CLS, FID/INP
Mobile and desktop results
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Website speed is measured in human attention spans. Research by Google consistently shows that as page load time increases from one second to three seconds, the probability of a mobile visitor bouncing rises by 32%. At five seconds, it rises by 90%. At ten seconds, by 123%. These are not abstract statistics, they translate directly to lost revenue, reduced conversion rates, and lower organic search rankings. Google has explicitly included Core Web Vitals (LCP, CLS, and FID/INP) as Page Experience ranking signals since 2021, meaning that a slow website is penalised algorithmically in addition to being abandoned by users. Testing website speed is the first step in diagnosing and closing the performance gap between your site and your competitors who have already invested in optimisation.
A complete website speed test measures several distinct phases of page loading, each with its own typical bottlenecks. DNS resolution time is usually negligible but can spike if you use a slow or unreliable DNS provider. Time to First Byte (TTFB) measures how quickly your server responds after a request, a TTFB above 800ms usually indicates slow server processing, inefficient database queries, or absent caching at the origin. First Contentful Paint (FCP) marks when the first content appears on screen. Largest Contentful Paint (LCP) marks when the dominant content element loads, this is Google's primary measure of perceived page speed. Cumulative Layout Shift (CLS) measures visual stability. Each metric has a specific threshold defined by Google: LCP should be under 2.5 seconds, CLS under 0.1, and INP under 200 milliseconds.
Understanding which metric is failing is far more actionable than fixating on a single composite score. A page with an excellent LCP but poor CLS may be fast to load but jarring to interact with, causing users to mis-tap and leave in frustration. A page with good CLS but poor LCP is visually stable but slow to show useful content, inviting bounces before the first paint completes. Use the full breakdown from the speed test to identify the specific metric requiring attention, then target your optimisation efforts at the corresponding cause rather than scattering effort across changes that may not move the needle on what is actually broken.
Speed testing should also inform a broader performance culture rather than serving as a one-off exercise. Build a habit of running tests at consistent intervals: before each significant deployment, after enabling any new third-party integration, and on a regular schedule for your top revenue and traffic pages. Save the historical results, even informally in a spreadsheet, so you can spot creeping regressions as new content, scripts, and plugins accumulate over months. A site that ships at 92 on mobile often drifts to 70 within a year if no one is paying attention, and recovering that lost ground is significantly harder than holding the line through routine measurement.
Enter any URL and click Test to get an instant website speed report.
Step-by-step guide to test website speed online free:
Enter the URL
Paste the full URL of the page you want to test, including the https:// prefix and any path segments. Avoid shortened links or tracker-laden URLs that may redirect, as each hop adds latency and obscures the true performance of the destination page you actually want to measure.
Select device type
Choose mobile or desktop depending on which audience matters most for your use case. Mobile is the default recommendation for almost every site because Google ranks predominantly on mobile signals, but desktop testing is still valuable for B2B tools, dashboards, and any product where the bulk of users sit on laptops or workstations.
Run the test
Click Test. The tool will load your page in a headless Chrome environment and measure key performance metrics from the moment the request is issued through to full rendering. Allow 20 to 40 seconds for the test to complete, longer for very heavy pages or those with many third-party scripts that take time to settle.
Review and act
Review the results carefully. Focus on any metrics in the red or failing range first, these have the highest impact on user experience and SEO and will deliver the biggest gains per hour of optimisation effort. Move on to amber metrics only once the failing ones have been pushed into safer territory, then validate everything with a retest.
Common situations where this approach makes a real difference:
Pre-launch website check
A developer finishing a client website runs a speed test before handing over to confirm all images are compressed, scripts are deferred, and total load time is under 3 seconds on mobile. They iterate on the failing metrics, retest, and only mark the project complete once the mobile Lighthouse score clears 80. This catches issues at the cheapest possible stage rather than after the client has already invited stakeholders to view a live but sluggish site, which would damage credibility and require an awkward second round of remediation work.
Post-update performance audit
A site owner installs a new WordPress plugin and immediately re-runs the speed test to confirm the plugin has not added significant page weight or blocking scripts. The before-and-after comparison reveals an extra 320KB of JavaScript and a 0.6 second LCP regression caused by the plugin loading on every page. Armed with that data, they configure the plugin to load only where needed, restoring the previous speed profile without sacrificing the plugin's functionality on the pages that genuinely use it.
Competitor analysis
An SEO consultant tests competitor websites to benchmark load times and identify performance advantages they could exploit in their client's ranking strategy. Discovering that three of five competitors score below 50 on mobile while the client sits at 78 reveals a defensible moat. The consultant turns the data into a slide deck for the client's next quarterly review, showing how sustained performance investment translates directly into improved organic visibility versus rivals who have neglected technical health.
Use this for a quick, comprehensive check of any website's loading performance, before launch, after changes, or when investigating a speed-related SEO issue.
Get better results with these expert suggestions:
Test the page your users actually land on
Homepage speed is rarely representative of your full site performance, especially on content-heavy or e-commerce sites where templates differ significantly. Test your top landing pages, product pages, blog posts, and category pages separately. These are the pages real users judge and that Google crawls and scores for search ranking purposes. A homepage that scores 95 means little if your highest-traffic product page scores 42 and represents 70% of paid search landings.
Compare mobile and desktop results separately
Google uses mobile-first indexing, so your mobile performance score is what determines your search rankings in nearly all cases. Test mobile performance as the priority and treat desktop as a secondary check. If your mobile score is significantly worse than desktop, your SEO performance is being dragged down by mobile-specific bottlenecks such as oversized images, JavaScript that runs slowly on weaker CPUs, or render-blocking resources that desktop networks can mask but mobile ones cannot.
Retest after every significant site change
A single plugin, third-party script, or new image format can significantly alter performance in ways the person making the change never anticipated. Build speed testing into your deployment process, test before and after every significant change to catch regressions before they reach production and affect your search rankings. The cost of catching a regression in staging is minutes; the cost of catching it in production after Search Console flags it weeks later can run into lost rankings and revenue.
Use HTTP Archive data to benchmark against competitors
httparchive.org publishes aggregate performance data for millions of websites broken down by category and technology stack. Use it to understand what performance scores are typical in your industry and set realistic improvement targets rather than optimising toward an arbitrary round number. If the median Shopify store scores 38 on mobile, hitting 65 already places you well above the field and the marginal cost of pushing further may not be justified by the marginal ranking gain.
Test from multiple locations if possible
Website speed varies significantly based on server location and CDN configuration. Testing from a location geographically close to your target audience gives the most representative result.
Run the test 3 times and average the results
Single speed test results can be skewed by temporary server conditions. Running 3 consecutive tests and comparing the results gives a more reliable baseline to work from.
Test both mobile and desktop
Google uses mobile-first indexing, so your mobile performance score is the most important for SEO. However, desktop speed still matters for users on those devices, test both.
More use-case guides for the same tool:
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