If you are checking your website speed performance through Google PageSpeed Insights and wonder why the Google score keeps changing (even when nothing changed on the site) this article provides an explanation as well as a comparison to how GTmetrix tests your website speed performance.
Google PageSpeed does not measure your site in a stable, real-world way like GTmetrix does.Instead, it:
- Simulates a very slow phone
- Google tests mobile using an emulated Moto G Power (budget Android)
- CPU is throttled
- Network is throttled to Slow 4G
- Adds randomness by design
- The test runs on shared Google infrastructure
- Each run may start with slightly different network latency
- A difference of 100–300 milliseconds is enough to move the score by 5–10 points
- The score is not linear
- The PageSpeed number is not a stopwatch
- It’s a weighted formula
- If a key metric crosses a threshold (even slightly), the score drops disproportionately
That’s why:
- for example 57 → 51 does NOT mean the site got slower
- It means the test crossed an internal threshold by a fraction of a second
Why GTmetrix looks “better”
GTmetrix:
- Uses a real high-end phone
- Uses consistent test servers
- Measures how fast the site actually renders
Google PageSpeed Insights:
- Uses emulation
- Uses artificial throttling
- Penalizes aggressively to push site owners toward extreme optimization
Both tools are valid — they just answer different questions.
Google PageSpeed is a diagnostic tool, NOT a speedometer. Small timing differences can cause visible score swings without affecting real visitors.
If you have any questions regarding this information please feel free to reach out to our Client Success team at success@haleymarketing.com.
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