With Google’s Core Web Vitals taking center stage when it comes to measuring the performance of a webpage, there are many other metrics that are part of the overall picture of what makes a top-performing webpage, and by extension, a brand’s website.
Core Web Vitals, when taken together, provide a powerful set of metrics that shape how your page is doing and how its responding to user interaction. It provides you with a broad view but it’s not the whole picture. To widen the lens you can incorporate non-Core metrics into your purview, which, when taken together, can greatly help to improve the performance of a page.
But what are these metrics that stretch beyond Core Web Vitals? Let’s take a look.
Speed Index (SI)
The speed index is a measurement that checks how fast the contents of a page become visibly populated during a load. The way that it’s calculated is by using frame-by-frame analysis on the page. It counts the visual progression that is made between frames that are captured every 100 milliseconds.
What’s my SI score?
Poor: 5.8 seconds or more
Okay: between 4.3 and 5.8 seconds
Good: 4.3 seconds or less
What’s making my SI perform poorly?
Essentially anything that is preventing the page from loading quickly is going to damage your SI score. That’s a lot of possibilities. For example, the main thread being blocked; or the use of rotating carousels, which worsen scores as they are continually changing.
How can I improve my SI score?
Tackling the issue of speed index isn’t a single-source solution. It’s going to take a collection of metric tweaks. Things that you can do include using lazy loading images, which are images that only load on the page once the user scrolls down, cutting down on bandwidth. This is also a useful tip because many page visitors don’t scroll down too far. And you can get rid of unnecessary downloads by taking a look at your page’s assets and deleting parts that are just not doing much and are better off thrown out.
Time to Interactive (TTI)
Time to Interactive is a measurement that checks how long it takes from when the page begins to load to when it’s fully interactive. And for a page to be fully interactive, it must be able to respond to user interactions within 50 milliseconds, have the most visible elements rendered, and be able to display the most useful content that’s measured by First Contentful Paint.
What’s my TTI score?
Poor: 7.3 seconds or more
Okay: between 3.9 and 7.3 seconds
Good: 3.8 seconds or less
What’s making my TTI perform poorly?
Like the Speed Index, there are likely multiple reasons why your TTI performance is dragging out your score. It’s also tied to other metrics like the First Contentful Paint, so that if the latter scores poorly so will the former.
How can I improve my TTI score?
How to compare the right way
If you’re sitting there thinking “okay, here are the most important metrics to keep in mind when analyzing a page’s performance. But now I need to compare them,” then keep in mind that there is a right way to compare metrics. Apple to apples, if you like, rather than chalk and cheese.
To get it right, we need to get the difference between field data and lab data, in addition to desktop and mobile data.
The field and the lab
Field data comes from the collection of data from real visitors, each with their unique network and device. Your field data may consist of 183 visitors from mobile and 430 from desktop, among which 573 have used Safari and 40 Google Chrome.
Lab data comes from the controlled environment that you have set up, using predefined variables like the location of the test, the browser, and the device.
As you can see these types of data are very different and produce very different results. So first know what you want to compare and specify. Do you want to compare Time to Interactive on mobile via Safari from San Francisco? Or do you want to compare Speed Index on desktop via Chrome from Frankfurt?
The worst thing you can do as an analyst is to think that you’re managing quality scores (from lab data) while overlooking the incredibly poor visitor performances (the field data).
The desktop and the phone
When you’re researching Core Web Vitals as well as the wider metric environment (which can seem more like a jungle that you’re in the middle of with no rope to lead you through the thickets) you will encounter a bunch of data that comes from desktop/laptop and mobile.
You’ll probably notice fairly quickly that desktop scores are generally better than mobile scores. That’s just how it is, because desktops have better and bigger hardware that is capable of faster speed as well as a more reliable internet connection.
Useful measuring tools
There are plenty of websites out there that can help you to measure your Core Web Vitals and the broader metric environment. These include:
Hopefully now there is greater clarity surrounding the wider web metrics that populate the background behind the Core Web Vitals that Google has structured when it comes to a webpage’s speed performance.