Google evaluates user experience using Core Web Vitals.

How Google Uses Core Web Vitals For Evaluating User Experience

In an attempt to make the internet more user-friendly, Google introduced a set of metrics in 2021 known simply as Core Web Vitals (CWV). These help website owners determine how well a webpage is performing and identify which areas need to be improved. The Google Core Web Vitals should not be confused with Web Vitals. These provide a more in-depth technical view of site performance. As a subset of the Web Vitals, the CWV are used to determine the user experience (UX) interactions common to website visitors. This is regardless of the type of website visited.

And when it comes to these core user experience metrics, Google looks toward loading time, interactivity, and visual stability. According to Google: “Web Vitals is an initiative by Google to provide unified guidance for quality signals that are essential to delivering a good user experience on the web. Site owners should not have to be performance gurus in order to understand the quality of experience they are delivering to their users. The Web Vitals initiative aims to simplify the landscape and help sites focus on the metrics that matter most, the Core Web Vitals.”

How To Measure UX With CWV

Measuring a website’s user experience involves three “core” metrics as follows:

  • Largest Contentful Paint (LCP): This Core Web Vitals metric looks at the perceived page load time speed by measuring the total amount of time it takes for the largest piece of content on the page (text or image) to load.
  • First Input Delay (FID): It measures the time needed for the browser to respond after the first user interaction.
  • Cumulative Layout Shift (CLS): This metric measures the visual stability of a given webpage while downloading. It also offers feedback in terms of how much the page’s layout shifts.
Measuring User Experience With Core Web Vitals


“Google believes that the Core Web Vitals are critical to all web experiences. As a result, it is committed to surfacing these metrics in all of its popular tools,” said Google, explaining the importance of these three metrics, in particular. The aim for any website owner is to get as high of a Core Web Vitals score as possible.

Google provides two types of Core Web Vitals measurements in the form of Field Data and Lab Data.

Field Data Measurements

Filed data, as its name implies, is a type of CWV measurement taken directly from website visitors using a Google Chrome browser. These users also need to give their permission to send anonymous UX data to Google. This data is used to generate a Chrome User Experience Report (CrUX). It’s important to mention that Page level data will not be included in the report if the page doesn’t reach at least 1,000 monthly visits. Using Google’s PageSpeed Insights tool will also gain you access to the filed data collected in the CrUX report. The Google Search Console also displays this field data, but it’s reported in a way that makes it easier to view Core Web Vitals-aggregated URLs.

Lab Data Measurements

Lab data, on the other hand, is made out of simulated CWV scores. Since there’s always some slight variance between test run results, many will run the test multiple times and average out the Core Web Vitals score. The aim of these reports is to get a diagnostic and improve page speed scores. Lab data scores can also be accessed through the Page Speed Insights tool, as well as other third-party tools that use the Google Lighthouse tool. Among these site speed testing tools, we can include the following:

These testing tools introduce a headless Chrome bot to the page to download, simulating the desired information. The Google Lighthouse tool uses artificial throttling to simulate how a mobile device would download a webpage. To put it differently, “these exact figures are defined in the Lighthouse constants and used as Lighthouse’s throttling default. They represent roughly the bottom 25% of 4G connections and top 25% of 3G connections (in Lighthouse this configuration is currently called “Slow 4G” but used to be labeled as “Fast 3G”). This preset is identical to the WebPageTest’s “Mobile 3G – Fast” and, due to a lower latency, slightly faster for some pages than the WebPageTest “4G” preset.”

Simulated network throttling can be achieved in four ways as follows:

  1. Simulated throttling: This is the method used by the Google Lighthouse tool.
  2. Applied throttling: Also known as Request-level throttling, this method isn’t as accurate as the simulation method above, but the Lighthouse algorithm compensates for that drawback.
  3. Proxy-level throttling: Since this method doesn’t affect the User Datagram Protocol (UDP), it’s considered to be the ideal technique.
  4. Packet-level throttling: While this is the most accurate form of throttling, it also tends to result in the most variances between tests. The Web Page Test tool employs this testing method.

Other Page Speed UX Metrics

Even though the Core Web Vitals are essential in measuring user experience, they are not the only metrics that need to be taken into consideration. Other Web Vitals metrics are available through such tools like Page Speed Insights. In fact, Google announced that it will launch a new metric called Interaction to Next Paint (INP). The INP looks at how long it takes for a user to interact with the entire webpage. This is what Google refers to as overall interaction latency.

Meta: The Core Web Vitals help website owners determine how well a webpage is performing and identify which areas need to be improved.

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