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Google's Core Web Vitals Set Clear Goals for User Experience

by Michael Krieger - May 26, 2021 - 2 minute read

Site speed has always been a nebulous concept. Google aims to change that with Core Web Vitals. 

The difference between a slow site and a fast one is largely a matter of perception, and there are no bright-line rules on how quickly a site should load.

Core Web Vitals are a set of metrics that reflect load time and user experience. But unlike other site speed measures, Google made Core Web Vitals an organic ranking factor as of May 2021.

With this carrot-and-stick approach, Google has provided an opportunity for digital marketers and web developers to align on a common set of metrics that can meaningfully improve user experience.

Check Your Vitals

There is no single way to measure page speed and user experience. Instead, there is a confusing glut of metrics such as response time, time to first byte, blocking time and more - each open to interpretation as to what, if any, impact they have on user experience.

What’s more, page speed tests can produce wildly different results due to location, network infrastructure, browser configuration, and a host of other external factors.

Google aims to simplify the landscape by doubling down on three specific usability metrics:

Largest Contentful Paint (LCP)

LCP is the classic load time measurement and examines the time it takes for the largest image or text block on the page to become fully visible.

  • Good: Less than 2.5 seconds
  • Needs Improvement: Between 2.5 seconds and 4 seconds
  • Poor: More than 4 seconds

First Input Delay (FID)

FID examines interactivity - specifically, the time between a user’s first interaction with the page (such as a link click) and the response (such as a page load).

  • Good: Less than 100 milliseconds
  • Needs Improvement: Between 100 milliseconds and 300 milliseconds
  • Poor: More than 300 milliseconds

Cumulative Layout Shift (CLS)

CLS is largely an experience metric. Have you ever moused over to a link and, a millisecond before you clicked, the page content shifted? Google measures this behavior and assigns it a score.

  • Good: Less than 0.1
  • Needs Improvement: Between 0.1 and 0.25
  • Poor: More than 0.25


Google tests Core Web Vitals compliance automatically while crawling the web, and site owners can review the results in Search Console. Here you can find detailed performance reports on both mobile and desktop URLs, as well as information on any pages that are not measuring up.

This is not the first time Google has used its influence to encourage usability standards. Other ranking factors such as mobile friendliness and intrusive interstitials were introduced in a similar fashion and have generally been viewed as a positive force on web development practices.

Core Web Vitals gives marketers and developers a common language with which to enact site improvements. It remains to be seen whether these metrics will substantively impact organic search rankings, but a faster web is a better web - that much is clear.

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