Mobile page speed vs Desktop

[Jako Basson]

Hi There.

I'm working on optimizing our eCommerce store front using page speed insights as my main metric.

On our desktop speed test I get a consistent 90 - 100 score.

On mobile however I only get around 20 - 40.

Here are some details below of the same run between mobile and desktop:

Desktop score 96:

• First Contentful Paint
  
• 0.7 s
• Speed Index
  
• 3.7 s
• Time to Interactive
  
• 0.8 s
• First Meaningful Paint
  
• 0.8 s
• First CPU Idle
  
• 0.8 s
• Estimated Input Latency
  
• 10 ms

Mobile score 26:

• First Contentful Paint
  
• 2.6 s
• Speed Index
  
• 10.9 s
• Time to Interactive
  
• 28.0 s
• First Meaningful Paint
  
• 3.0 s
• First CPU Idle
  
• 10.9 s
• Estimated Input Latency
  
• 30 ms

So my question is, how is there such a massive difference between mobile and desktop, specifically the Time to Interactive and the CPU Idle?

When I test on my mobile device or on chrome mobile emulation, i don't get close to anything as slow as what page speed insights shows.