Skip to main content

Speed Index

What Speed Index measures​

Speed Index measures how quickly the page's visual content is displayed during the loading.

A page that begins rendering elements after 1s and finishes at 5s will have a better Speed Index than a page that also finishes at 5s but only starts rendering at 4s.

Speed Index is expressed in seconds but should be treated as a score. It doesn't correspond to a single event on a timeline.

How to improve Speed Index​

Anything you do to improve overall load speed will generally improve Speed Index. Two factors have a particularly strong impact:

  • TTFB (Time To First Byte): reducing the wait for the first byte lets visual elements appear sooner.

  • JavaScript and secondary loads that work on:

    • Reducing JavaScript execution time
    • Reducing the browser's work to render the page (DOM complexity, CSS classes, etc.).

Scoring​

Scoring guideline:

Good< 2s
Fair2s to 5s
Poor> 5s