# How to carry out a website speed test Website loading speed is a crucial success factor. Even a delay of just a few seconds can determine whether users stay on a page or leave. A website speed test shows not only how fast a page loads, but also what is slowing it down. ### Key Takeaways A website’s loading speed is crucial for conversion rates and Google rankings. - Key metrics for measuring speed are the Core Web Vitals, such as `LCP`, `CLS` and `INP`. - Tools such as PageSpeed Insights, Lighthouse and GTmetrix test performance. - Test reports and waterfall charts reveal long load times and blocking resources. - Quick wins include image formats such as `WebP`, caching and a hosting check. ## Why is website speed important? A fast website can improve conversion rates because users are highly sensitive to loading times. Even a one-second delay can affect revenue. As loading time increases, bounce rates also tend to rise because visitors lose patience and may leave for a competitor’s site. Performance is especially important for e-commerce, online stores and landing pages, where page speed can directly affect business success. Speed is also an important signal for search engines. Google uses Core Web Vitals as one of many ranking factors to **assess user experience**. As a result, slower pages can struggle to rank well. Website performance is also important for mobile users, who may be browsing on slower or less stable connections. ## How to test website speed using metrics To run a website speed test and measure performance reliably, you need to look at a few key metrics: - **Largest Contentful Paint (LCP)**: Largest Contentful Paint measures when the largest visible content element on a page has loaded. It indicates when the main content of the page appears fully loaded to the user. - **Cumulative Layout Shift (CLS)**: Cumulative Layout Shift measures the visual stability of a page. It shows whether content moves unexpectedly while the page is loading, which can quickly frustrate users. - **Interaction to Next Paint (INP)**: Interaction to Next Paint measures how responsive a page is during a user’s visit. It replaced First Input Delay (FID), which only measured the response to the first interaction. INP gives a broader view of how quickly a page reacts to user input. Together, these metrics provide a realistic picture of the user experience and can help you optimise your website for better speed and usability. ## What tools can you use for a website speed test? There are several tools you can use to measure website performance. Just be aware that they do not all work in the same way. In general, there are two main approaches: synthetic monitoring, which tests a page under controlled conditions, and real user monitoring (RUM), which analyses performance data from actual visitors. Together, these two methods give you a more complete view of how your website performs. ### CA App Synthetic Monitor (Broadcom) The CA App Synthetic Monitor is a widely-used synthetic monitoring tool for professional use. It simulates website visits **from more than 120 monitoring locations around the world**, allowing you to test load times, availability and transaction flows under controlled conditions. The tool is especially useful for complex web applications and multi-step processes. It provides detailed technical metrics and waterfall analyses, and companies often use it for SLA monitoring and early warning systems. However, it can be complex for beginners. ### Google PageSpeed Insights [PageSpeed Insights](https://www.ionos.com/en-ie/digitalguide/online-marketing/search-engine-marketing/google-pagespeed-insights/) combines lab data with insights from real users. This means it shows how a page performs under controlled test conditions and how real users experience it. The results are also clearly broken down by Core Web Vitals. Google provides specific tips for optimising website performance. One particularly useful feature is that you can test **both mobile and desktop versions** of a page. This makes PageSpeed Insights a good choice for a quick website speed test. ### Lighthouse Lighthouse is an open-source tool from Google that’s **built into Chrome DevTools**. You can use it to run a website speed test, but also to check other important areas like accessibility and SEO. Lighthouse uses synthetic monitoring under controlled conditions and is useful for developers in the optimisation phase. The reports are detailed and technically focused, so some background knowledge is helpful. ### GTmetrix GTmetrix combines Lighthouse data with additional proprietary analyses. It provides clear waterfall charts and load time timelines, making it easier to understand how a page loads. Depending on the plan, users can **choose test locations, browsers and connection speeds**. The ability to compare previous test results is also useful because it lets you track performance changes over time and identify fluctuations. GTmetrix is a good option for beginners as well as advanced users. ## How do you interpret a test report? A website speed test report usually includes metrics, charts, and specific optimisation recommendations. To interpret the results correctly, go through them step by step: 1. First, focus on the **Core Web Vitals** because they show how users experience a page’s loading speed, responsiveness and stability. Values in the green range are a good sign, while yellow or red indicators show where optimisation is needed. 2. Next, look at the **total load time and when the content becomes visible and usable**. These values can give you an initial indication of issues related to hosting quality, caching or large files. 3. Then, **analyse the waterfall charts**. They show which files load in which order and how long each request takes. Long bars often point to large images, uncompressed scripts or slow server responses. Resources that block the early loading process are particularly important because they can delay the rendering of the entire page. 4. After that, distinguish between **critical and non-critical resources**. Not every file has to load immediately for the page to be usable. Tracking scripts, animations and external services can often load later or asynchronously. 5. Finally, review the tool’s **optimisation recommendations**. Not every warning points to a serious problem. The goal is to remove the biggest performance bottlenecks with as little effort as possible. ## A quick checklist for website speed testing Not every performance optimisation requires major technical changes. In many cases, a few specific measures can noticeably improve website speed. The following checklist gives you a quick overview of common areas to review: **Optimise images**: Use modern formats such as WebP and make sure images are sized correctly. **Use caching**: Browser and server caching reduce load times for returning visitors. **Check hosting**: Server performance, location and resources can have a major impact on website speed tests. **Combine monitoring**: Instead of choosing between synthetic monitoring and real user monitoring, use both. Synthetic monitoring is useful for controlled testing, while RUM shows how real visitors experience your website. This is a markdown version of: [https://www.ionos.com/en-ie/digitalguide/websites/web-development/test-website-speed/](https://www.ionos.com/en-ie/digitalguide/websites/web-development/test-website-speed/) for AI/LLM consumption.