Everything You Need to Know About Google's Core Web Vitals Update

In August 2021, Core Web Vitals will raise the bar for page performance when it becomes the newest addition to Google’s algorithm. In simple terms, the set of signals – which measure how people experience your website – will become one of the markers Google uses to determine page rankings.

Improving page performance using Core Web Vitals metrics will safeguard and improve your site’s organic visibility, and help you maximise user engagement and conversions. According to research conducted by Portent, conversion rates drop by an average of 4.42% with each additional second of load time (between seconds 0-5). Naturally, this has a huge impact on your brand’s ability to turn sessions into sales.

Learn how to improve page performance and grow revenue with our Core Web Vitals tips.

What Are Google's Core Web Vitals?

According to Google, Core Web Vitals make it easier to measure and improve the on-page experience of your website. They are:

Page Load Speed

LCP, or Largest Contentful Paint, measures page load speed (specifically, the time it takes to load the largest content element in the viewport). For a good user experience, LCP should occur within 2.5 seconds of when a page first starts to load. 


FID, or First Input Delay, measures how long it takes a browser to respond to a user interaction, for example click a link or tap a button. For a good user experience, FID on a page should be less than 100 milliseconds.

Visual Stability

CLS, or Cumulative Layout Shift, measures the visual stability of a page as it loads. For a good user experience, pages need a CLS of less than 0.1.

To maintain a positive page experience, Google suggests you meet these conditions for 75 percent of website visitors.

Core Web Vitals sit alongside a group called Web Vitals, which evaluate user experience metrics like mobile friendliness, safe browsing, https and intrusive interstitials (aka pop ups). Performing well across both sets of metrics will help you to gain a good page experience ranking. This, when combined with existing ranking factors – such as domain authority, relevant content, SEO, links and site structure – will determine your Google ranking.

How To Measure Core Web Vitals 

In preparation for the changes, Google has baked Core Web Vitals into their suite of tools. The Chrome User Experience Report (CrUX) is a good place to start, as it measures anonymous user data for each condition without the need to install analytics on your pages. This report fuels key tools like Google PageSpeed Insights, which provides a visual snapshot of page load speed, and the Search Console, which offers a detailed overview of how well every page on your site is meeting the Core Web Vitals.

For a deeper look, creating a CrUX Data Studio Report in Google Data Studio will allow you to visualise Core Web Vitals data in a meaningful way, before taking the necessary steps to optimise performance.

Outside the Google ecosystem, some analytics tools have in-built reporting metrics for Core Web Vitals, while others require you to build custom reports. For granular analysis at scale, use third party web crawler Screaming Frog with a Google Page Speed Insight API to retrieve speed recommendations and CLS scores at page level. 

How Should Your Brand Prepare for This Algorithm Update? 

Your website developers can take several steps to improve performance across these metrics.

Page Load Speed (LCP)
The most effective way to meet page load speed standards is to review resource delivery and take steps to optimise, defer or remove any elements that slow this down. 


  • Optimising server efficiency 

  • Routing users to a nearby Content Delivery Network (CDN) 

  • Caching assets and serving HTML pages cache-first 

  • Deferring non-critical JavaScript and CSS and minifying CSS 

  • Establishing third-party server requests early 

  • Optimising and compressing images 

  • Compressing text files 

Interactivity (FID)

First Input Delay measures how quickly a browser responds to user actions. To optimise for FID, you must ensure each web page responds in less than 100 milliseconds (as outlined by Google). 

Slow FID is often caused by heavy JavaScript. In other words, too much code needs to load before the page is usable. To combat this, optimise how JavaScript parses, compiles and executes on your website. Try breaking down long tasks, reducing JavaScript execution time, optimising pages for interaction readiness and using a web worker. 

Visual Stability (CLS)

Poor visual stability is frustrating for users, as it makes page elements move around during loading. The visual stability metric, Cumulative Layout Shift, works to capture this by measuring page content stability.

To improve visual stability, address the common root causes, including: 

  • Images without dimensions

  • Ads, embeds and iframes without dimensions

  • Dynamically injected content

  • Issues with web fonts

  • Actions waiting for a network response before updating

With Google on a mission to help users find the most relevant sites with the best user experience, you can expect ongoing updates to Core Web Vitals.

If you need to improve rankings, drive organic traffic and maximise engagement, Revium can help. Contact us today.