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.
John Mueller Hangout Transcript
The lab data in Google Search–Google’s Speed Insight results are the same as Lighthouse results in my Chrome browser. Do they use the same formula?
I don’t know 100 percent. But they are done completely differently, in the sense that if you use PageSpeed Insights, that is run on a data center somewhere with essentially emulated devices where we try to act like a normal computer. And we have restrictions in place that make it kind of like a little bit slower and normal internet connection, those kinds of things. And in Lighthouse, it basically runs on your computer with your internet connection. And I think Lighthouse within Chrome also has some restrictions that it applies to make it a little bit, I don’t know, maybe a little bit slower than your computer might be able to do, just to make sure that it’s comparable.
But essentially these run in completely different environments, and that’s why you would often see different numbers there. If you test with PageSpeed Insights, you see one number. If you test in Lighthouse and your browser, you might see different numbers. If you test with other speed tools that run online, you might see different numbers. Also the field data, the data that we actually use for search ranking that you see in Search Console, that can be also completely different numbers just because your users might have on average, a different kind of device or a different kind of internet connection. So even if the formulas are the same, the whole environment around these systems is very different.