Page speed & Webtracking

Enlightened: Core Web Vitals in a nutshell

Core Web Vitals are THE new core metrics for Google. Together with other metrics they constitute the ranking factor “Page Experience”:

Core Web Vitals consist of three KPIs used to evaluate the usability of websites:

• Speed: Largest Contentful Paint (LCP)
• Interactivity: First Input Delay (FID)
• Stability: Cumulative Layout Shift (CLS)

Let’s take a brief look at the key metrics below:

Largest Contentful Paint: How fast does the website load?

Largest Contentful Paint (LCP) measures the loading time that passes until the largest content element (images, videos, text blocks) in the visible area of your website is loaded.

Google defines the following values:

• good: up to 2,5 seconds
• needs improvement: 2,5 – 4 seconds
• bad: 4+ seconds

The loading status determines which the largest content element of your website is. The largest element is usually loaded at the end. The following is an example of our JENTIS website:

You can find all the details and the exact calculation basis of the LCP here in the Google documentation on Largest Contentful Paint.

First Input Delay: When can the user interact with the website?

In a nutshell: First Input Delay (FID) measures the amount of time that elapses between the first user interaction with the website and the browser response.

When you visit a website, you may click a button without waiting for the website to fully load. However, the browser usually does not react at that time because it is busy loading the website. To prevent users from jumping off now, the FID measures how much delay passes between the user input and the browser’s response. The main factor for the calculation is the “Time to Interactive”.

Google defines the following values:

• good: up to 100ms
• needs improvement: 100-300ms
• bad: 300 ms or more

You can find all details about the FID here in the Google documentation about the First Input Delay.

Cumulative Layout Shift: How stable is the website?

In a nutshell: The Cumulative Layout Shift (CLS) indicates whether and to what extent unexpected layout changes occur while the user interacts with your website.

Unexpected layout changes happen when layout shifts occur as the site loads, and elements slide down as other elements are reloaded. This can have undesirable consequences for the user.

Google defines the following values:

• good: 0.1
• needs improvement: 0.1-0.25
• bad: 0.25 or more

All details and the exact calculation basis of the CLS can be found here in the  Google documentation on the Cumulative Layout Shift. So much for the definition of the Core Web Vitals (LCP, FID, CLS). Now let’s go into practice:

How to retrieve the Core Web Vitals

You can check how well your website is performing either via Google Lighthouse, the Google Search Console or directly in Google PageSpeed Insights. Simply enter your domain in the input field and click on “analyze”.

After a few seconds you will receive information on whether your website has passed the evaluation according to the Core Web Vitals – or not.

You also get a speed score for mobile and a speed score for desktop. This score is between 0 and 100, where 90-100 is good, 50-80 needs improvement  and below 49 is bad.

Tip: Since March 2021, Google indexes only “mobile first”, it is important that your speed score fits mobile. As a result, it usually automatically fits for desktop as well.

The result of the Core Web Vitals is provided as field data and lab data. Field data is anonymous data of real users on different devices and with different connection speeds. Lab data is simulated data on a single device and with a fixed network connection.

Depending on the results, you will receive a set of recommendations from Google that can be used to reduce the loading time of your website, as well as a prediction of how many seconds it can be reduced by:

What are the biggest optimization levers?

Every single recommendation from Google is a good optimization lever. However, you have to put costs and benefits in perspective (as always). Google still values good content the most. So before you invest tens of hours to make your website 100 ms faster, it probably makes more sense to invest this time in good, user-friendly content.