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6.9.2021

6 min read

A guide to Core Web Vitals (CWV)

Core Web Vitals are Google’s new performance metrics that directly impact website search rankings. Here’s what you need to know.

A graphic illustration of Google’s three Web Core Vitals

Illustration by Anita Goldstein

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There's a new set of performance assessments coming down the pike for Google's search ranking algorithm. Core Web Vitals (CWV) is taking its place in Google's search algorithm—and as this change rolls out, website creators and owners need to learn how to leverage Core Web Vitals to deliver faster-loading sites with better user experiences.


A high-performing site drives increased interaction, improved visitor satisfaction and ultimately, more conversions for your site. Let’s take a closer look at Core Web Vitals, along with a few other key performance measures, to understand what they mean for your site and visitors.



1. The importance of user experience


Your visitors come to your site ready to explore the experience you've crafted for them—but they'll never enjoy what you've built if it takes too long to load. Users will bounce from even the most captivating webpages if they're stuck waiting for them to finish loading.


This is one reason why Google is emphasizing website performance, meaning speed, as a ranking factor on its search engine. When all other factors such as credibility and authority are comparable, faster sites rank higher in search results.


The relative simplicity, transparency and actionable insights of Google’s Core Web Vitals make an excellent resource for understanding and monitoring your site's performance.



2. Understanding Core Web Vitals


Core Web Vitals is a new set of assessments based on field data (anonymized data collected from actual visits to your sites) designed to standardize and simplify how site owners monitor three key elements that impact site performance: loading time, interactivity and visual stability. Because these metrics are based on actual user data, Core Web Vitals scores are fluid and change as users interact with your site.


Core Web Vitals assessments are shown as both numerical scores and simple labels, so you can see at a glance how well your site is performing.


  • Good CWV scores mean everything is happening quickly and smoothly. This means your user experience is doing just fine.

  • Needs improvement CWV scores alert you to issues that may be slowing down your site.

  • Poor CWV scores warn when your UX is seriously falling down on the job.


Core Web Vitals assesses three essential UX aspects that affect how fast your site performs:


  • Loading: Largest Contentful Paint (LCP) analyzes the time it takes to render the largest visible image or text block. To be in good standing, your LCP should be within 2.5 seconds of a user landing on your page.

  • Interactivity: First Input Delay (FID) refers to the time it takes for the browser to process the event handlers of a user’s first interaction with your page. FID measures page responsiveness and interactivity, with a “Good” rating equaling no more than 100 milliseconds. Note that FID only measures the "delay" in event processing; it does not measure the event processing time itself nor the time it takes the browser to update the user interact after running event handlers.

  • Visual Stability: Cumulative Layout Shift (CLS) measures the visual stability of your site. It can be frustrating and harmful to your site experience if calls-to-action or forms unexpectedly shift as users click, so aim to keep your CLS score under 0.1.



A graph showing the three Core Web Vitals by Google: Largest Content Pain (LCP), First Input Delay (FID), and Cumulative Shift (CLS)