Quality Score:
90 - 100
50 - 89
0 - 49
*Source: PageSpeed Insights
Above is an example of scoring for Google PageSpeed Insights. The scores are assigned in the following four categories:
1. Performance
2. Accessibility
3. Best Practices
4. SEO
If there are any issues or scores less than 100, the tool will inform you of solutions to correct.
For each category, Google recommends achieving a Mobile score of 90 - 100 to ensure a user-friendly / mobile-friendly experience for your visitors.
To clarify, high or low scores do not necessarily reflect search engine rankings. Instead, the scores correlate to crawlability and bounce rates, which could affect rankings.