How Website Speed Tests Work

Updated: 2022-05-24 / Article by: Timothy Shim

You may be familiar with the saying that “a picture is worth a thousand words.” Well, it turns out that a single second is worth about 3.4% of conversions for your website. That's a massive amount of lost business due to slow loading pages. 

So how can you determine if your website is loading fast enough? Website Speed Tests are a great way to find out, but there are a lot of different tests you can use.

This article will provide you with information on running speed tests properly, interpreting the results, and using the information to improve your website speed.

How to Test Website Speed Correctly

You can use many tools to run a website speed test. Some will give you a lot of information, and some might not give you enough. The best way to get the most accurate results is to use a couple of tools or run multiple tests via the same means. 

Latency Explained
Data travel time is constrained by physical distance. Actual server response times vary for different server locations.

It is important to remember that results are often dependent on your web server location in relation to the origin point of the test. The further apart these two are, the longer the time data needs to travel, potentially affecting speed test results.

Because of this, you should always choose a web server near the location where you expect the most visitors. For example, a website serving primarily US-based traffic should be somewhere within the US.

If you cater to a global audience, then running a website speed test from several test locations can give you a better idea of how the distance affects visitors from various locations.

Ideal Server Speed Test Methodology

Your test methodology should involve several runs and look something like this:

  1. Run a test from location 1 and repeat 3 times, recording the results from all the tests.
  2. Repeat the process from another test location, similarly recording the data. I recommend that you test from at least three strategic areas; the US, Europe, and Asia.

Recommended Website Speed Test Tools

Website Speed Tests Example
Example – Website speed tests we did for our test sites hosted at Interserver (more details here) from different locations using WebPageTest.org

The tools that give the most information about your site's performance use real, human visitors to test your website speed. For example, Pingdom's Full Page Test uses real browsers (IE9, Chrome, and Firefox) in real locations (US, Australia, Europe) to load your site and provide performance reports.

Because it tests your site as a complete entity, including all objects on the page, it can offer suggestions for improving performance and insight into what could be slowing down your site.

However, there are many other useful website speed test tools you can consider, including:

For a complete list of these tools, check out our List of 20 Free Website Speed Test Tools.

Understanding Speed Test Terminology

A website speed test is helpful in many ways, but only as long as you understand how to use the results. Only by knowing what the data means can you implement the proper corrections to improve the performance of your website.

Before we dive into interpreting speed test results, it's helpful to be familiar with some terms. These terms are mainly associated with networking.

Latency

The time taken for everything that happens between the time you click a link or enter an address in your browser and when you see the results appear on your screen. The standard measurement of Latency is in milliseconds (ms).

Ping

Often confused with Latency, Ping is a precise term used to describe the time it takes for a single packet of data to leave your computer and reach its destination. Like Latency, you measure Ping in ms.

First Byte or Time to First Byte (TTFB)

TTFB is a measurement used to indicate the responsiveness of a web server. You measure TTFB as the duration from the user or client making an HTTP request to the reception of the first byte by the client's browser. 

Page Size

The size of a web page is the size of all its contents. For a web browser to completely load a web page, it must download all contents, including HTML code, images, style sheets, etc. The larger the sum of these contents, the more time it will take to load.

First Interactive

Most web browsers will allow users to start performing activities on a website before fully loading. First Interactive is the amount of time on your website before this can happen.

Depending on the website speed test tool you choose, you will likely encounter more terms. These include:

And more. Try to learn as much as possible about what these terms mean if you intend to use a test that provides the above data.

Interpreting Speed Test Results

Google’s PageSpeed Insights provides a quick assessment of your website performance.

As you can see from the above terminology, it can be difficult to apply one method of interpretation to all website speed test tools.

Because of this, I'm going to use one tool as an example – Google PageSpeed Insights.

Google PageSpeed Insights is excellent since Google provides it and will most likely demonstrate what the search giant prefers. It is also extremely user-friendly, giving visual results and advice on addressing issues discovered.

Google tests separately for Mobile and desktop performance and focuses on four key elements: First Contentful Paint (FCP), First Input Delay (FID), Largest Contentful Paint (LCP), and Cumulative Layout Shift (CLS).

Each area tested will return a result in seconds and a quality indication bar. Green means good, orange means needs improvement, and red requires more urgent attention.

Scrolling down the page will provide a breakdown of the individual test areas and the factors contributing to each. You can use this to make surgical improvements to your website.

Also Read

Troubleshooting Slow Website Speed Test Results

Speed Test Result Data - Waterfall Chart
Waterfall charts, usually provided by most great speed test tools, show detailed progression of web page element loading, allowing you to see what occupies more time. 

Most slow websites are the result of similar sets of deficiencies. For example, high CLS timings result from failing to optimize images properly. Yet, given the number of areas needing attention, it's impossible to cover these comprehensively.

Some common problems and solutions include:

Reduce unused JavaScript

Dynamic websites (like those run on WordPress ) often encounter this problem. You can address the issue by using a good cache plugin to reduce JavaScript redundancy.

Reduce the impact of third-party code

Many websites today are modular and use components from various developers (for example, Google, Facebook, Fonts, etc.). This combination often results in a lack of cohesion that affects performance. Streamline your website and use as few different code sources as possible.

Reduce initial server response time

Essentially, Google is telling you that your web server sucks. Sub-par web hosting often results in poor speeds, and there's little you can do except move to another hosting provider.

Image elements do not have explicit width and height

Many website owners make the mistake of simply uploading images without further amendments. When uploading images, specify the parameters to avoid confusing web browsers and causing load time delays.

Serve images in next-gen formats

For images, not only are dimensions important, but so is the image format. Next-gen formats like WebP increase compression, making images faster to download over the web.

Serve static assets with an efficient cache policy

Some content is downloaded and kept on their browser when visitors load your website. This process helps improve performance for repeat visits. Setting cache policies lets browsers know how long they should retain those images before repeating a request.

Avoid an excessive DOM size

DOM refers to the size of your web page. Getting an excessive DOM warning means you need to consider streamlining the page. You can do this in many ways, such as reducing the number of images on the page or using fewer sections.

Avoid large layout shifts

Dynamic websites generate page sections on-the-fly. When you have many of these resizable elements on a page, the layout will frequently shift, resulting in a poor user experience. Where possible, define page elements properly.

The possibilities are endless. Before trying to fix these issues one by one, I recommend you consider thoroughly optimizing your website. There are many universally accepted performance enhancements that website owners need to implement.

To learn more, read WHSR's guide on improving your website performance.

Final Thoughts on Website Speed Tests

Website speed tests are a great way to get a snapshot of your website's performance. These tools are easy to use and generally provide relatively accurate data. Of course, it also helps that many excellent website speed test tools are free.

However, it is essential to remember that the operative word in the statements above is “snapshot.” Website speed tests are static, and minor changes to your website can change results significantly. Because of that, it's better to schedule periodic performance assessments of your website and rectify newly discovered problems as soon as possible.

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About Timothy Shim

Timothy Shim is a writer, editor, and tech geek. Starting his career in the field of Information Technology, he rapidly found his way into print and has since worked with International, regional and domestic media titles including ComputerWorld, PC.com, Business Today, and The Asian Banker. His expertise lies in the field of technology from both consumer as well as enterprise points of view.