How to Test Page Speed

How These Tools Work

These speed testing tools use a bunch of browsers to load websites and replicate a web visitor’s experience across varied geographic locations. Speed traps are monitored across various elements of the web page being tested: including file size, load time, response time, and requests pertaining to specific website parts (JavaScript, CSS files, HTML, images, etc.).

Each tool generates a unique performance score based on a set of rules with Web page performance and user priorities in mind. Suggestions are generated for page speed improvements that generally speaking, if you implement fixes for these on your site, you should see a decrease in your overall load times. For example, if a large image file is loaded uncompressed, speed testing tools would recommend that you compress the bulky file. They don’t tell you how to compress the image, that’s where I come in, simply that you should compress it to achieve a faster page load time/testing score.

What to Test?

Time to First Byte (TTFB) : Simply put, is a measurement of how long the browser has to wait before receiving its first byte of data from the hosting server. The longer it takes to get that data, the longer it takes to display your page.

Largest Contentful Paint (LCP) [Google Core Web Vital] : LCP measures how long it takes for the largest content element (e.g. a hero image or heading text) on your page to become visible within your visitors’ device screen. Aim for an LCP of 1.2 seconds or less.

Total Blocking Time (TBT) [Google Core Web Vital] : TBT tells you how much time is blocked by scripts during your page loading process. Aim for a TBT of 150 milliseconds or less.

Cumulative Layout Shift (CLS) [Google Core Web Vital] : CLS indicates how much layout shift is experienced by visitors as your page loads. Ads, poor coding, not including image dimensions, are some common CLS culprits. Aim for a CLS score of 0.1 or less.

Requests: This is the total number of internal and external file requests that are made to the server in the process of loading the website. The smaller the better. This number is helpful for verifying that after removing an unnecessary plugin or after optimizing scripts or enabling lazy-loading on images, seeing this number decrease verifies it is working.

Total Bytes or Page Size: As the name suggests, this is the total size of all the code and image files it takes to render the page. Less is more. Sites that use Page Builders or Poorly Coded Themes might see a huge number here. Page sizes can range from well optimized at 100KB to on average 1MB to ridiculously bloated at 2+MB.

WebPageTest.org example of where to find the Recommended What To Test metrics.
WebPageTest.org – Where to find the Recommended What To Test metrics.
GTmetrix Core Web Vitals metrics
GTmetrix.com – Where to find the Recommended What To Test metrics.
Google PageSpeed Insights - Where to find the Recommended What To Test metrics.
Google PageSpeed Insights – Where to find the Recommended What To Test metrics.

Different tools – Google’s Page Speed Insights, Web Page Test and GTMetrix, among others – identify different issues, test different performance metrics – as you see above, not one tool has all the metrics easily viewable, and indicators in different ways, from different browsers and geographic locations. Performance ratings and test results are therefore bound to be different, and no single tool identifies every single performance bottleneck in website designs. There’s useful information to glean from each of the three listed herein.

How to Properly Run a Website Speed Test

Speed Test Location Matters

Almost every speed test tool allows you to choose from different testing locations around the globe, and this matters quite a bit. The reason is that this is all relative to the data center where your WordPress site is hosted. TTFB, network latency, all come into play. 

It’s important to speed test your site both from a location that is close to where your website is hosted and one that is far away. For example, my host is NameHero and has their data centers (server locations) in Michigan. I’ll need to keep this in mind when I’m selecting a testing location for each of the three Speed Testers. I’ll choose one that’s centrally located and then one from Either the East or West Coast for comparison.

Whatever you do, be consistent with the locations you choose for each testing tool.

WebPageTest.org – Setting the Test Location and Browser.
WebPageTest.org – Setting the Test Location and Browser.

WebPageTest Locations to Use:

  • Salt Lake City, Utah – GCE (Chrome/Firefox)
  • Virginia – EC2 (Chrome/Firefox)
  • Los Angeles, CA – (Chrome/Firefox/Opera)
  • Dulles, VA (Desktop/Android/iOS)

WebPageTest Browser to Use:

  • Chrome
  • iPhone X
  • Google Pixel 2XL
GTmetrix.com – Setting the Test Location and Browser.
GTmetrix.com – Setting the Test Location and Browser.

***Register for a Free account with GTmetrix to access 7 global test locations, including 1 US based. Otherwise, all of your tests will default to Vancouver, Canada.

GTmetrix Locations to Use:

  • San Antonio, TX

GTmetrix Browser to Use:

  • Chrome

PageSpeed Insights doesn’t let you choose testing conditions.

You Have to Test Multiple Times

The big problem is that many users tend to only run a speed test once, the content isn’t cached on the WordPress host or CDN yet, and then it appears that the site is actually slower. This can also happen if you just cleared your WordPress site or CDN’s cache.

To properly speed test, you need to see everything load from cache (both from your WordPress host and CDN if you have one). How to make sure your site is loading from the cache in the speed tester? Before speed testing the page, in your browser, visit the page you want to test repeatedly in a couple different tabs/windows. This ‘wakes up’ the Cache for that page. You’ll notice that each time you load it, it’s getting faster. That means you’re ready to now test the page in a Speed Tester. To get an accurate reading in the Speed Tester, it requires running your speed test multiple times. I have found that 3 tests each tool works.

Which Tool to Pick?

Now it’s time to dive into the different website speed test tools you can use. What’s the optimal load time that you should be aiming for? Well, the faster the better, but Google suggests that around 2 seconds or less is a good target. Each tool has its own set of different metrics and therefore you can’t compare one tool’s test results to another. No tool is perfect.

WebPageTest speed tests from multiple locations around the globe using real browsers (IE, Chrome, etc) & mobile too. Test with real browsers on their computers. The best tool for a deep understanding of your site. Tests 6/6 recommended metrics from above!

GTmetrix is easy to use and beginners can pick it up quite fast. You can create a free account and save the last 20 tests, compare historical data, and more. Test with real browsers on their computers. The best tool for keeping track of your speed over time. Tests 3/6 recommended metrics from above, only free mobile test is in Canada.

Google PageSpeed Insights measures speed on mobile and desktop. It’s the best tool for testing your Core Web Vitals, which will be an SEO ranking factor starting May 2021. Test with simulated browsers on their computers. Tests 3/6 recommended metrics from above. Doesn’t allow you to set a location.