After the introduction of Lighthouse into our lives, the number of performance criteria directly affecting topics like UX and SEO has increased. The evaluations done by looking at a few points on the page in the old Google Pagespeed setup have been improved with the methods developed by Google engineers over the years. In this article, we will try to examine how the Lighthouse score is calculated.
As of 2024, the performance criteria for Lighthouse version 10 are as follows:
- First Contentful Paint - 10%
- Speed Index - 10%
- Largest Contentful Paint - 25%
- Total Blocking Time - 30%
- Cumulative Layout Shift - 25%
The most significant innovation compared to the previous version, Lighthouse 5, is the addition of CLS (Cumulative Layout Shift). This metric, which was announced to be an important performance criterion for SEO as of June 2024, may become very critical in the coming years.
Lighthouse has also prepared a tool that shows you in advance what kind of score you can achieve by entering your page speed goals. You can access the Lighthouse score calculation tool here.
If you ask which number ranges the color coding is based on, you can check the ranges below. Seeing green in these evaluations will mean you have succeeded:
- 0-49 (poor): Red
- 50-90 (needs improvement): Orange
- 90+ (good): Green
Scores vary for mobile and desktop sites, but with mobile traffic surpassing 75%, evaluations are made based on the mobile score.
You might encounter different results in each Lighthouse test. Some reasons for this include ads and the types of ads on the page, A/B tests conducted within the site, instant changes in internet traffic, and instant situations that may occur on the server.
The easiest way to perform a Lighthouse test is to use the Chrome browser. Enter the "Inspect" menu, click on the "Lighthouse" tab, and then click the "Generate Report" button. The calculation, which will take about 8-10 seconds, is done by considering different devices and internet speeds.
