Difference values between PageSpeed Insights and Google Search Console - Speed (experimental)

Question

I like your website and it does a good job, but when I analyze my website in PageSpeed Insights, I get a 96 for mobile and a 98 for desktop, and when I look in Google Search Console (GSC), it rates my mobile website as moderate, presumably between 50-89, and the desktop as "not enough data".

Why is there that much of a difference between PageSpeed Insights and GSC? And is Google ranking my site poorly because GSC looks to be getting a poor score? Does the location of my server make any difference to the score? Should it be near the Search Console's server to receive a better score/rank?

Answer 1

So the issue you are experiencing is because of how PSI processes data to calculate your score vs how Search Console does.

If real world data is available Search Console will prioritise that over the simulated data to calculate your scores (which makes sense), PSI will always use the speeds it calculates under 'lab data'.

The real world data is more accurate but you need to read it correctly to know how to improve it.

The 3 bars (green, orange and red) show data as follows for First Contentful Paint (FCP) and First Input Delay (FID):-

• FCP green: less than 1 second
• FCP orange: 1 to 3 seconds
• FCP red: over 3 seconds

and

• FID green: less than 100ms
• FID orange: 100ms to 300ms
• FID red: over 300ms.

These are calculated for the 75th percentile for FCP and 95th percentile for FID. (although not technically correct think of it as 3 in 4 people will have this experience or better for FCP and 19/20 people will have a better experience than shown for FID).

This is where you get a 'moderate' score in Search console.

The average break down for FCP is around 23%, 58% 19% respectively. You get 36%, 45%, 19% so you are pretty close to the average.

Similar story for FID.

What to look at

You have quite a variance on FCP, there are lots of possible causes of this but the most likely ones are:-

1. You have a lot of visitors from other countries and aren't using a CDN (or at least not to it's full potential).
2. The site is receiving spikes in traffic and your server is hitting capacity, check your resource logs / fault logs on the server.
3. Your JavaScript is CPU heavy (230ms FID says it might be) and part of your page render depends on the JS to load. The simulated runs do a 4 times CPU slowdown, in the real world some mobile devices can be up to 6-8 times slower than desktop PCs so JS differences start to add up quickly.

Test it in the real world

Simulated tests are great but they are artificial at the end of the day.

1. Go and buy a £50 android device and test your site on 4G and 3G and see how the site responds.

2. Another thing to try is open up Dev tools and use the performance tab. Set 'network' to '3G' and 'CPU' to '6x slowdown' and observe how the site loads. (after pressing the record button and refreshing the page). If you have never used this tab before you may need to search for a couple of tutorials on how to interpret the data but it will show JS bottle necks and rendering issues.

3. Put some load time monitoring JS into the page and utilise your server logs / server monitoring software. You will soon start to see patterns (is it certain screen sizes that have an issue? Is your caching mechanism not functioning correctly under certain circumstances? Is your JS misbehaving on certain devices?)

All of the above have one thing in common, more data to pinpoint issues that a synthetic test cannot find.

Summary / TL;DR

Search console uses real world data when you have enough of it, PSI always uses lab data from the run you just completed.

PSI is a useful tool but is only there for guidance, if Search console says your site is average you need to examine your speed using other real world methods for bottlenecks.