Google Core Web Vitals Basics: Everything You Need To Know

In May 2020, Google announced a new set of metrics called “Web Vitals.” These metrics are designed to help web professionals and site owners optimize websites for high quality real-world user experiences. Whether you manage a portfolio of sites, a single business website, personal blog, eCommerce site, or an information portal, understanding this new initiative – and more specifically, Core Web Vitals, which Google announced it will soon include as ranking signals in its search algorithm – can help you find opportunities to improve your site and boost your SEO efforts.


Web vitals are metrics that help Google provide some unified direction on what it considers the foundations of an excellent website experience. This should be seen as a welcome development since web developers, designers and digital marketing professionals certainly want to provide the best possible experience to site visitors. 

Even though Google has provided numerous tools to measure performance (and there are lots of non-Google tools out there), it can be difficult to keep up with the standards of the day for each one. To combat this confusion, the web vitals initiative aims to simplify this broad landscape and provide a list of the most important metrics with quantified scores under one roof.


Core Web Vitals are a subset of web vitals that apply to every website and every page within that site. Each core web vital represents a specific factor in an overall website experience and provides a desired benchmark based on the real-world experience of a typical site visitor. 

While the metrics that help to define Core Web Vitals will continue to evolve in the coming months and years, Google has presented a set of three primary areas every webmaster and site owner should pay attention to going forward.

These three significant areas of the user experience are:

  1. Visual stability
  2. Load time
  3. Interactivity 

And here are the corresponding Core Web Vitals that Google has identified as presently important in quantifying and qualifying these areas of the user experience:

  • Largest Contentful Paint (LCP) — Loading (How fast your site appears on the screen)
  • — Interactivity (How fast your site reacts to the input of a user)
  • Cumulative Layout Shift (CLS) — Visual Stability (How much things are moving on the screen while the site is loading)


Before we dive deeper into these three metrics, let’s have a quick look at First Contentful Paint, which can be thought of as a precursor to today’s Core Web Vitals. Google first announced First Contentful Paint (FCP) in early 2019 as one of two performance metrics to evaluate the speed ranking of a website.

First Contentful Paint marked the first entry point in the load timeline for any specific page where the end user can begin to see anything on their screen. This was an imperfect metric as it did not give any indication about when most meaningful content of a website would become available to a user; however, Google realized that, even though FCP was flawed, developers, site owners and digital marketing professionals needed more of these types of metrics if they were going to make meaningful improvements to the experiences on their websites. 

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Now let’s jump briefly into the different aspects of Core Web Vitals and dig into what each one measures. While these can seem like overly technical terms to some, don’t focus too much on the specific terms as much as what each is actually measuring.

Largest Contentful Paint (LCP)

Largest Contentful Paint (LCP) measures the point at which the largest element of content appears on the screen when a page is loading. 

For instance, if you have a web page with plain text, some headings, subheadings and a large picture, the largest elements of your web page (which would most likely be the image) would be considered as the Largest Contentful Paint. Since it is the largest piece of content on your website, it is destined to make a significant impression on the site visitors. 

By getting the image to load quicker and faster, you can make your site appear optimized to Google. Sometimes, optimizing might be as simple as decreasing the load time of images by compressing them or using different file formats. 

LCP is relatively easy to understand and interpret, but it’s important to note that it does not measure the time it takes to fully load the entire web page. It only measures when the largest element of content appears to users. Four factors that website owners can focus on to ensure best LCP practices are: slow response times from the server, load times for various resources, rendering on the end user side, and JavaScript and CSS blocking.

First Input Delay (FID)

The First Input Delay measures the time it takes for the website to respond whenever the user interacts. This is a key performance indicator because the faster a website loads and is functional, the better chance you have that a user will remain on the page.  If website owners aim to offer an exceptional user experience to their website visitors, the website’s FID is something you’ll certainly want to focus on. 

Delays tend to happen when the browser is still working in the background. A browser is not supposed to do everything at once. Sometimes, it holds certain requests until the current request is processed. For many JavaScript heavy sites, as an example, it is hard for some browsers to display the elements and content quickly. 

To improve a website’s FID, Google says to focus on the following:

  • Reduce the impact of third-party code
  • Reduce JavaScript execution time
  • Minimize main thread work
  • Keep request counts low and transfer sizes small

Cumulative Layout Shift (CLS)

The third core web vital is a brand new combination of metrics — Cumulative Layout Shift (CLS). This metric determines your site’s visual stability by measuring how many times elements (copy, images, audio files, video, etc.) jump while they are loading. 

For example, let’s say that there is a button loaded on the screen that is inviting users to click on it. However, in the background, a large picture is stopping users from taking that very action. 

What is the likely end result? The moment you try to click on the button, the screen scrolls down a little bit, and instead, the image opens up. 

Layout shifts happen mostly when there are ads embedded or loading on the site. Even though ads contribute to the bottom line of some websites, if they are not properly matched to the pages, it can affect the overall website’s layout. 

To calculate and assign layout shift scores, the browser looks at the viewport size and the movement of unstable elements in the viewport between two rendered frames. According to Google, the layout shift score is a product of two measures of that movement. These are the impact fraction and the distance fraction.

Google says that anything that scores below 0.1 is considered good. Anything between 0.1 to 0.25 seconds is room for improvement.


These three core web vitals (largest contentful paint, first input delay and cumulative layout shift) will soon become some of the basic metrics to measure the loading, interactivity, and visual stability of your website. 

While there is still some time before these changes go into effect as ranking signals, they will happen and website owners should begin to dive deep into the backend of their websites and make the appropriate improvements now. The sooner you improve your website’s score in each of these new metrics, the better.

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