Core Web Vitals

Core Web Vitals are three specific metrics Google uses to measure the real-world experience of loading and using a web page: how fast it loads, how quickly it responds to input and how stable it is visually.

What Core Web Vitals Means in Marketing

Google added Core Web Vitals as a ranking signal through its Page Experience update, which rolled out across 2021 and 2022. The signals are collected from real Chrome browser sessions, not simulated tests, so they reflect what actual users experience on actual devices and connections.

The three metrics:

• Largest Contentful Paint (LCP): measures when the largest image or text block on the page becomes visible. Google considers anything under 2.5 seconds good. Over 4 seconds is poor.
• Interaction to Next Paint (INP): measures the delay between a user input and the visual response. Under 200 milliseconds is good. Over 500 milliseconds is poor. INP replaced the earlier First Input Delay (FID) metric in March 2024, because FID only measured the first interaction while INP measures all of them.
• Cumulative Layout Shift (CLS): measures how much visible content unexpectedly moves while the page loads. A score under 0.1 is good. A page where images or ads load late and push text down is the classic CLS problem.

How Core Web Vitals Works

Google collects these from the Chrome User Experience Report (CrUX), which aggregates anonymised performance data from Chrome users who have opted into browser reporting. If your site has enough traffic, this field data will appear in Search Console. Sites with insufficient traffic see only lab data from tools like PageSpeed Insights.

The most common causes of poor scores:

• LCP: large unoptimised images, slow server response times, render-blocking JavaScript or CSS, no lazy loading for off-screen images.
• INP: heavy JavaScript on the main thread that blocks the browser from responding to input, excessive third-party scripts.
• CLS: images and ad slots without defined dimensions, dynamically inserted content above existing content, web fonts that swap visibly on load.

Core Web Vitals Example

A media site that relies on display advertising is a common victim of CLS problems. Ad networks inject content into the page after load, and if the layout does not reserve space for those ads, every insertion shifts the content. Readers click on the wrong thing or lose their place in an article. Reserving the space in the layout, even before the ad loads, brings CLS under control without removing the ad revenue.

Why Core Web Vitals Matters for Marketers

Poor page experience directly affects conversion rates. A slow-loading product page costs you sales before the ranking question even enters the picture. The business case for fixing Core Web Vitals runs on its own without SEO: faster pages sell more.

The SEO case adds to it. In competitive categories where ranking differences are small, page experience can be the marginal factor. It is one of the few technical signals you control directly, which makes it worth the engineering investment.