What Is Speed Index?


The speed index is a performance metric that measures how quickly the contents of a page are visibly populated. It’s an essential metric for measuring perceived performance because it captures the end-user experience: how fast content is visible during page load. 

The lower the speed index, the better. In this article, you will learn how to calculate and improve the speed index score. Let’s dive in!

How can the speed index be calculated?

A speed index score can be calculated using one of two methods: synthetic or real user monitoring (RUM). 

The synthetic speed index is calculated by running a script in a browser and capturing video footage of the page loading. This video footage is then analyzed to determine how long it takes for each visible element to appear on the screen. 

Real user monitoring (RUM) calculates speed index by tracking actual users as they load a page. The data collected includes how long it took for each visible element to appear on the screen for each user. This data is then used to calculate the speed index score. 

Synthetic and RUM speed index scores are represented in milliseconds and have no upper limit; however, lower scores are generally better. A good rule of thumb is that your speed index should be less than 1000 ms.

How to improve the speed index score?

There are a few key things you can do to improve your speed index score:

1. Make sure your pages are as lean and clean as possible – reducing the number of HTTP requests, minimizing code, and using a content delivery network.

2. Use browser caching effectively – ensure the browser caches your static content, so it doesn’t have to be re-downloaded on each page view.

3. Optimize your images – use image compression and reduce the number of images on each page.

4. Minimize redirects – each redirect adds additional time to the page load process.

5. Enable gzip-compression – this will compress your HTML, CSS, and JavaScript files, so they take up less space and load faster.

If you want to improve your website performance, don’t hesitate to contact our dedicated team!

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