Core Web Vitals Explained

Why Core Web Vitals Are a Google Ranking Factor

Since Google's Page Experience update, Core Web Vitals are official ranking signals. Pages that score "Good" on all three main vitals gain a ranking advantage over slower competitors.

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LCP — Largest Contentful Paint

LCP measures when the largest visible element (usually a hero image or heading) finishes loading. Google's Good threshold is under 2.5 seconds. Poor LCP (above 4s) directly lowers your Page Experience score and rankings.

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INP — Interaction to Next Paint

INP replaced FID in March 2024 as the responsiveness metric. It measures the delay between a user interaction (click, tap, key press) and the next visual update. Good is under 200ms. Heavy JavaScript is the most common cause of poor INP.

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CLS — Cumulative Layout Shift

CLS measures how much the page layout unexpectedly shifts during loading. A score below 0.1 is Good. Common causes include images without dimensions, ads that inject above content, and web fonts causing text to reflow.

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TTFB — Time to First Byte

TTFB measures how quickly your server responds to a request. Good is under 600ms. Slow TTFB cascades through all other metrics since the browser can't start loading anything until it receives the first byte from the server.

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Mobile Scores Are What Matter Most

Google uses mobile-first indexing — your mobile Core Web Vitals scores are what primarily affect your search rankings. Desktop scores still matter for user experience but carry less SEO weight than mobile performance.

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Pass All Three to Get the Ranking Boost

Google's Page Experience signal requires passing LCP, INP and CLS — all three must be in the "Good" range to receive the full ranking boost. Passing two out of three gives partial credit but the biggest gains come from clearing all three.

Frequently Asked Questions

What are Core Web Vitals and why do they matter?

Core Web Vitals are a set of metrics defined by Google to measure real-world user experience on web pages. They focus on three dimensions: loading performance (LCP), interactivity (INP), and visual stability (CLS). Since May 2021, these metrics have been official Google ranking signals as part of the Page Experience update. Pages that score "Good" on all three gain a ranking advantage over competitors with poor scores.

What is the difference between LCP and FCP?

FCP (First Contentful Paint) measures when the first piece of content (any text, image, or element) appears on screen. LCP (Largest Contentful Paint) measures when the largest visible element — usually the hero image or main heading — finishes loading. LCP is the more important metric for user experience since it represents when the page feels "loaded." LCP is a Core Web Vital; FCP is a supporting diagnostic metric.

What replaced FID (First Input Delay)?

Google replaced FID with INP (Interaction to Next Paint) in March 2024. FID only measured the delay on the first interaction, while INP measures the responsiveness of all interactions throughout the entire page lifecycle — clicks, taps, and keyboard presses. INP provides a much more complete picture of how responsive a page feels to users. The Good threshold for INP is under 200ms.

How do I fix poor LCP?

The most impactful LCP fixes are: (1) Preload the LCP image using <link rel="preload">, (2) Compress and convert images to WebP or AVIF format, (3) Serve images via a CDN, (4) Remove render-blocking CSS and JavaScript that delays the LCP element from loading, (5) Improve server response time (TTFB). The LCP element is usually a hero image — identify it using Chrome DevTools or PageSpeed Insights and optimize it specifically.

How do I fix Cumulative Layout Shift (CLS)?

The most common CLS fixes are: (1) Set explicit width and height attributes on all images and videos so browsers reserve space before they load, (2) Avoid inserting content above existing content (ads, banners, cookie notices), (3) Use CSS aspect-ratio boxes for media embeds, (4) Use font-display: swap with size-adjust to minimize layout shift from web fonts, (5) Reserve space for dynamic content loaded via JavaScript. The goal is to prevent any element from unexpectedly moving after the page initially renders.

Do Core Web Vitals affect all websites or just some?

Core Web Vitals apply to all pages indexed by Google, across all industries and website types. However, the ranking impact is most significant when competing pages are otherwise roughly equal in quality and authority — in those cases, Core Web Vitals can be the tiebreaker. For highly competitive, content-driven industries (news, e-commerce, SaaS), even small improvements in vitals can produce measurable ranking and traffic gains.

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Why Core Web Vitals Are a Google Ranking Factor

Frequently Asked Questions