What are Core Web Vitals?

Core Web Vitals: the three metrics at a glance

Core Web Vitals is Google’s umbrella term for the metrics that matter most from the perspective of real visitors: How quickly does the main content appear, how fast does the page respond to clicks, and does the layout jump around while loading?

Since March 2024, INP has replaced the earlier FID metric. For each metric, Google has published fixed thresholds at which a page counts as “good.” Measurements are taken separately for mobile devices and desktop—the mobile view usually matters most, because performance and connections there are often weaker.

• LCP (Largest Contentful Paint): time until the largest visible element has loaded—good means up to 2.5 seconds
• INP (Interaction to Next Paint): response time to clicks, taps and input—good means up to 200 milliseconds
• CLS (Cumulative Layout Shift): a measure of unexpected layout shifts—good means a score of up to 0.1

How Core Web Vitals are measured

Google distinguishes between field data and lab data. Field data comes from real Chrome users and is collected in the Chrome User Experience Report (CrUX). A page passes the assessment if at least 75 percent of page views meet the thresholds.

Lab data simulates a page view under fixed conditions, for example with Lighthouse. It helps with troubleshooting but does not always reflect reality. PageSpeed Insights gives you a quick overview of both, while Google Search Console shows the trend for your entire website.

The benefits of good scores—and their limits

Fast, stable pages are more pleasant to use. Visitors find what they are looking for faster and abandon less often—especially on mobile and with a weak connection. For online stores and inquiry forms, that has a direct business impact.

At the same time, you shouldn’t overestimate the metrics: Google stresses that relevant, helpful content matters more. Core Web Vitals are one ranking factor among many and tend to tip the scales when content is of comparable quality. A perfect score is no substitute for a good page.

Improving Core Web Vitals: typical measures

Common causes of poor scores are oversized images, too much JavaScript, slow servers and late-loading elements without reserved space—such as cookie banners or ad slots. A few targeted changes can often deliver noticeable improvements without touching the design.

An example: on the home page of a skilled trades business, a large hero image loads at full camera resolution. Once it is compressed, scaled appropriately and loaded with priority, LCP often improves significantly—without any visible loss of quality. Nano Concepts analyzes Core Web Vitals during relaunches and as part of technical SEO and implements the optimizations directly in the code.

• Compress images, serve them in modern formats such as WebP or AVIF and size them correctly
• Remove unneeded JavaScript or load it later
• Use caching and a CDN, and reduce server response times
• Reserve fixed heights for images, videos and banners
• Preload fonts selectively and fine-tune fallback fonts