What Is Speed Index and How to Improve It

Short answer

Speed Index measures how quickly content is visually displayed during page load. A lower score means the page appears to load faster to users.

How it works

Speed Index captures video frames of the page loading and calculates the average time at which visible parts of the page are rendered. It rewards progressive rendering.

Example

A page that shows a skeleton screen immediately and fills in content gradually will have a better Speed Index than a page that stays blank until everything loads.

Why it matters

Perceived performance influences user satisfaction more than total load time. Speed Index reflects the visual progress users experience.