What is Speed Index and how can we improve its score?

In this tutorial we are going to say in simple language what is Speed Index or SI inside Gtmetrix tool and what to do with this error? How to improve? Is this an error?

I am the author of this article, I am Pouria Ariafar from **SEO teaching**, this is not a translation article from other sites, we tried to gather a good article for you from the knowledge and experience we had along with a series of reputable sites. We are happy to be with us.

In the previous article we talked about what is Largest Contentful Paint and how to optimize it, we also talked about what is First Contentful Paint and now we are going to talk about Speed Index which is strongly dependent on these two previous articles, FCP and LCP.

The Speed Index, unlike the previous ones, was not introduced by Google this time, but was introduced by the WebPageTest site. Be sure to look at the article on the best speed testing tool on our site and this tool is one of the best. After a few years, Google brought Lighthouse into Google, and after a while, the Gtmetrix tool considered this as one of its factors.

It is noteworthy that speed factors are no longer as simple as in the past, and to solve many of these SEO factors requires high expertise (in the field of programming and SEO and sometimes UX) and just reading a few Persian and foreign articles is not a special task. کرد. I said this first so that we do not expect too much from ourselves or the article at one time, otherwise we will say everything we know, as in the past. 😉

## What exactly is Speed Index or SI?

Before I say what Speed Index is, what does Above the Fold mean? Above the Fold The first part of the site that you see, the same part that is at the top of the site and we first see it and then scroll down and where we need to go.

Another definition of above the fold for better understanding: is the part of the page that is placed in front of the user’s eyes after the site is loaded and without scrolling.

Now the Speed Index measures how quickly the top half of our page, or Above the Fold, completes visually.

So the Speed Index depends on the size and type of our browser. For this reason, it is different from criteria such as FCP and LCP, and unlike them, it is not a turning point in loading and displaying our page.

The Speed Index measure is obtained from frame-by-frame analysis of the page when loading and expresses the user experience during this time. Therefore, considering the Speed Index value, gives us a good understanding of the page speed status. In fact, the numerical value of SI does not give us useful practical information. But because it is directly or indirectly related to other criteria, it determines whether the optimization of these criteria is effective or not.

Now let me be a little more precise with the photo:

If we draw the completeness of a page over time, we end up with something like the image above. The blue line is the first site and the red line is the second site. The handle that both reached the same point at the end, but the blue reached much earlier.

Now to calculate the SI or the same Speed Index, we can curve like a picture above in a chart below and calculate the progress of each.

They use the logarithm to calculate the Speed Index and then convert it to a percentage. We do not talk much about how to calculate and its formula here, but as you can see, after calculating the second site or the same red, it is about 8-9 times slower than the number. It has the first site. (Photo source + more details)

## What is the value of Speed Index in the Performance Report?

The Speed Index score is 15% of the Performance Score in GTmetrix. How to score GTmetrix to SI, as follows:

- Less than 1.3 seconds: Good
- Between 1.3 and 1.7 seconds: Acceptable, but requires optimization
- Between 1.8 and 2.3 seconds: Slightly longer than standard
- More than 2.3 seconds: Much longer than standard

### How to optimize SI or Speed Index?

Most optimizations that affect FCP or LCP also improve the Speed Index. Also some of the ways to reduce Speed Index time include the following:

- Reducing JavaScript execution time
- Removing unused JavaScript files
- Replacing heavy JavaScript libraries with smaller alternatives
- First Contentful Paint optimization
- Largest Contentful Paint optimization

However, do not think that you can easily improve this factor, and you should know that to optimize it, it is effective in more than 20 cases, as we said in previous articles.

### Summary Speed Index

The Speed Index measures how quickly page content is visually visible; Especially the content in Above the Fold.

The timing of this criterion depends on the type of our browser. Also, this criterion is not a turning point that can be measured at a particular moment. But is calculated by mathematical formulas. So SI is more of a laboratory standard than a field standard.

But like the other criteria in the Performance section, it targets the discussion of user experience, and therefore, Speed Index optimization is important.

We can also tell from the Speed Index whether the optimizations we made to other GTM metrics and errors were effective. Because Speed Index is a comprehensive measure that is affected by other criteria and errors and is not an independent measure.

To improve SI, you have to check a series of important factors, which are at least 20, and we mentioned in **SEO teaching**, in other words, improving and optimizing the SI factor by giving a code is not solved and is not simple.

Finally, it is recommended that you seek help from an SEO expert or someone you trust and know to get better results. You can also ask questions in the comments of **SEO teaching** site.

Be sure to follow the instructions for fixing **SEO teaching** gtmetrix errors. Or if you are interested in technical SEO, follow the technical and technical SEO topics.

**Article author:** **Naser Rasouli** / SEO expert and consultant