Speed Index
What Speed Index measures​
Speed Index measures how quickly the page's visual content is displayed during load.
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​
Reducing the wait for the first byte lets visual elements appear sooner.
JavaScript and secondary loads​
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 |
|---|---|
| Fair | 2s to 5s |
| Poor | > 5s |