Why Does My Mobile Speed Score Differ from Google PageSpeed?

Answer

There can be a discrepancy between the Mobile Speed score displayed in Siteimprove SEO and the score shown in Google PageSpeed. The reasons for this are data type and measurement locations. Siteimprove uses the Lighthouse API to perform mobile speed checks, while Google PageSpeed uses additional data sources and may perform measurements from different locations.

Symptoms

You may experience one or more of the following:

• The Mobile Speed score in Siteimprove SEO differs from the score shown in Google PageSpeed.
• The same page receives different performance scores across the two tools.
• Mobile performance results appear inconsistent when comparing Siteimprove SEO and Google PageSpeed.

Prerequisites

Before reviewing this issue, ensure that:

• You have access to the Mobile Speed score in Siteimprove SEO.
• You have access to Google PageSpeed results for the same page.
• You are comparing results for the same URL.
• You understand that performance testing tools may use different methodologies and testing environments.

Cause

Data Type

Google PageSpeed uses both real-world data available in the Chrome User Experience report and lab data. Google Lighthouse uses lab data only to measure your website's performance.

• Lab data = simulated data.
• Real-world data = actual data.

Because the underlying data sources differ, the resulting scores may also differ.

Measurement Location

Another factor affecting the results is that the default settings for the location from where checks are performed might be different.

For example, when you're using PageSpeedInsights and run it from the browser, it chooses the location closest to you. With Lighthouse API, the locations may not be the same.

Because tests may be performed from different locations, the performance results may vary.

Resolution

No action is required.

Differences between the Mobile Speed score displayed in Siteimprove SEO and the score shown in Google PageSpeed are expected due to differences in:

• Data type.
• Measurement location.

When comparing scores, consider the methodology used by each tool before interpreting the results.

Additional Information

We use Lighthouse API to perform mobile speed checks in SEO. There can be a discrepancy between the mobile speed displayed on the platform and the speed shown when using Google PageSpeed. The reasons for this are data type and measurement locations.