Speed Index

Speed Index

Speed Index (SI) is one of the many metrics tracked by the Performance Scan on both desktop and mobile. Each metric captures a different aspect of your application's performance.

The resulting SI is shown in milliseconds:

What does SI measure?

The SI metric measures how quickly content is visually displayed during page load.

PageSpeed makes screenshots during the page load and computes the visual progression between those screenshots. The SI score is based on the differences in those screenshots.

How can I improve my application's SI score?

Known issues that have a large impact are:

• Minimize main thread work
• Reduce JavaScript execution time
• Ensure text remains visible during Webfont load

I would like to learn more

For more info on the SI metric, you can read this article on https://web.dev.