One SEO professional was curious about their page speed numbers across different tools: Google’s lab data vs. PageSpeed Insights results vs. Lighthouse results in the Chrome Browser.
Their main question was whether each of these tools used the same formula?
John replied that he doesn’t know 100 percent. However, even if they did use the same formula, they each work entirely differently.
Firstly, if you use PageSpeed Insights, it’s run on a data center somewhere with emulated devices. Google uses these emulated devices and tries to act as if they were a normal computer.
There are restrictions in place that allow Google to make it look like the connection is slower, and like a normal internet connection, and so on.
With Lighthouse, it runs on your own computer with your own specific connection to the internet.
These tools run in entirely different environments, Mueller said, and this is why you would see different numbers on a regular basis.
With PageSpeed Insights, you would see one number. If you use Lighthouse and your browser, you may see different numbers. Also, field data, the data that Google uses for ranking in Search Console, can be entirely different numbers because users may be using a different type of device or even internet connection.
Even with the same formulas, the environment surrounding these systems is extremely different, thus resulting in different numbers.
This happens at approximately the 37:35 mark in the video.