What are Core Web Vitals? Google's Page Experience Signals

Core Web Vitals are a set of specific metrics that Google uses to measure the real-world user experience of a web page. Introduced in 2020 and integrated into Google's ranking algorithm in 2021, these metrics focus on three critical aspects of user experience: loading speed, interactivity, and visual stability. They are part of Google's broader "page experience" ranking signals and represent one of the few areas where Google has been explicitly transparent about what it measures and what thresholds it considers good.

The Three Core Web Vitals

Largest Contentful Paint (LCP)

LCP measures how long it takes for the largest visible content element on the page to finish loading. This is typically a hero image, large text block, or video. LCP is a proxy for perceived loading speed: it answers the question, "When does the page feel like it has loaded?"

Good: LCP occurs within 2.5 seconds of when the page first starts loading.
Needs improvement: LCP is between 2.5 and 4.0 seconds.
Poor: LCP is greater than 4.0 seconds.

Common causes of poor LCP include slow server response times, render-blocking JavaScript and CSS, slow resource load times, and client-side rendering bottlenecks.

Interaction to Next Paint (INP)

INP replaced First Input Delay (FID) as a Core Web Vital in March 2024. While FID only measured the delay of the first interaction, INP measures the responsiveness of the page throughout the user's entire visit. It records the latency of all click, tap, and keyboard interactions, then reports a value near the worst-case scenario (the 98th percentile).

Good: INP is 200 milliseconds or less.
Needs improvement: INP is between 200 and 500 milliseconds.
Poor: INP is greater than 500 milliseconds.

Poor INP is typically caused by long-running JavaScript tasks, excessive DOM size, complex event handlers, and heavy main-thread work during interactions.

Cumulative Layout Shift (CLS)

CLS measures the visual stability of a page by quantifying how much the visible content shifts unexpectedly during loading. If you have ever been reading an article and had the text jump as an ad loaded above it, or tried to click a button only to have it move at the last second, you have experienced layout shift.

Good: CLS score is 0.1 or less.
Needs improvement: CLS is between 0.1 and 0.25.
Poor: CLS is greater than 0.25.

Common causes of layout shift include images without explicit width and height dimensions, ads or embeds that resize dynamically, late-loading web fonts causing text reflow (FOUT/FOIT), and dynamically injected content above existing content.

How Core Web Vitals Affect Rankings

Google confirmed that Core Web Vitals are a ranking factor as part of the page experience update. However, it is important to understand the nuance: content relevance still matters more. Google has stated that great content can rank well even with suboptimal Core Web Vitals, but when two pages have similarly relevant content, the one with better page experience will likely rank higher.

In practice, Core Web Vitals serve as a tiebreaker and quality signal. They are most impactful in competitive keyword spaces where many pages offer similar content quality. Improving your Core Web Vitals will not magically take a thin content page to position one, but it can give a well-optimized page the edge it needs to outrank similar competitors.

How to Measure Core Web Vitals

There are two types of Core Web Vitals data:

Field Data (Real User Metrics)

Field data comes from actual users visiting your site. Google collects this through the Chrome User Experience Report (CrUX), which aggregates anonymous performance data from Chrome users. This is the data Google uses for ranking purposes. You can access it through:

Google Search Console: The Core Web Vitals report shows which URLs have good, needs improvement, or poor scores.
PageSpeed Insights: Shows both field and lab data for any URL.
CrUX Dashboard: Historical trends via Google Data Studio.

Lab Data (Simulated Testing)

Lab data comes from controlled testing environments and is useful for debugging and development. Note that lab data cannot measure INP (which requires real user interactions). Lab tools include:

Lighthouse: Built into Chrome DevTools, provides a comprehensive performance audit.
WebPageTest: Advanced testing with various network conditions and devices.
FreePageRank: Our free SEO checker includes performance analysis as part of its 21-point website audit.

How to Improve Core Web Vitals

Improving LCP

Optimize your server: Use a CDN, enable caching, and ensure fast server response times (TTFB under 800ms).
Eliminate render-blocking resources: Defer non-critical CSS and JavaScript. Inline critical CSS.
Optimize images: Use modern formats (WebP, AVIF), appropriate sizing, and lazy loading for below-the-fold images.
Preload key resources: Use <link rel="preload"> for your LCP image or font.

Improving INP

Break up long tasks: Use requestAnimationFrame or setTimeout to yield to the main thread.
Reduce JavaScript: Remove unused code, defer non-essential scripts, and use code splitting.
Optimize event handlers: Keep interaction handlers lightweight and move heavy computation to web workers.
Minimize DOM size: Large DOM trees slow down interaction processing.

Improving CLS

Set explicit dimensions: Always include width and height attributes on images and videos.
Reserve space for ads: Use CSS to define minimum heights for ad containers.
Avoid inserting content above existing content: New elements should appear below the viewport or in reserved spaces.
Use font-display: swap carefully: Preload fonts and consider using font-display: optional to eliminate layout shift from font loading.

Check Your Core Web Vitals

Understanding your current Core Web Vitals performance is the first step toward improvement. Run a free analysis with FreePageRank to see how your site performs across key performance metrics, along with actionable recommendations for improvement. Our tool evaluates page speed, rendering performance, and numerous other factors that contribute to your overall page experience score.

Conclusion

Core Web Vitals represent Google's most explicit guidance on the user experience metrics that affect search rankings. By optimizing for LCP, INP, and CLS, you improve not only your chances of ranking higher but also the actual experience of every visitor to your site. Focus on serving fast, responsive, and visually stable pages, and you will be well-positioned for both current and future search algorithm updates.