What Are Core Web Vitals? The Metrics That Affect Your Google Ranking

If you've had a website for a while, you may have seen "Core Web Vitals" mentioned in reports or tools - often with red or amber scores. These are real Google ranking signals, not just numbers to ignore. This guide explains what they are, why they matter, and what you can actually do about them.

What Are Core Web Vitals?

Core Web Vitals are three specific measurements Google uses to judge how a page experience feels to a real visitor - focusing on loading speed, visual stability, and responsiveness. Google confirmed in 2021 that these are ranking signals, which means a page with poor scores can rank below a similar page with better scores.

The three Core Web Vitals are:

1. Largest Contentful Paint (LCP) - Is your main content appearing quickly?

LCP measures how long it takes for the largest piece of visible content - usually a main image or headline - to fully appear on screen from the moment someone starts loading the page.

Good: Under 2.5 seconds
Needs improvement: 2.5 to 4 seconds
Poor: Over 4 seconds

A slow LCP means your visitors are staring at a blank or partial page. If people leave quickly without interacting, a poor LCP is often part of the reason.

2. Interaction to Next Paint (INP) - Does your page respond quickly?

INP (which replaced an older metric called First Input Delay) measures how quickly your page responds when a visitor taps, clicks, or types. It looks at the slowest interactions throughout the whole visit, not just the first.

Good: Under 200 milliseconds
Needs improvement: 200 to 500 milliseconds
Poor: Over 500 milliseconds

A page that feels "frozen" or sluggish when you tap a button is showing a poor INP score.

3. Cumulative Layout Shift (CLS) - Does your layout stay stable?

CLS measures how much content jumps around while the page is still loading. If an image pops in late and pushes the text down just as you're about to tap a button, that's a layout shift - and it contributes to a poor CLS score.

Good: Under 0.1
Needs improvement: 0.1 to 0.25
Poor: Over 0.25

Poor CLS is the reason you sometimes accidentally click the wrong link on a page that's still settling.

Why Do Core Web Vitals Matter for Your Business?

They affect your Google rankings. Google treats them as a ranking signal - a "tiebreaker" between pages with similar content. A good score can give you an edge; a poor one can cost you positions without any other obvious reason.

They directly affect conversions. A slow or unstable page frustrates visitors before they see your offer. Research consistently shows that faster, more stable pages convert better - more enquiries, more purchases, more sign-ups.

They matter most on mobile. The majority of UK web traffic comes from mobile devices, where connections are slower and screens are smaller. Core Web Vital problems are typically more severe on phones than on desktop.

How to Check Your Core Web Vitals

• Google PageSpeed Insights (free) - enter your URL and get both a simulated score and real-world data from Chrome users, along with specific suggestions for improvement.
• Google Search Console - if your site is set up here, the Core Web Vitals report shows which pages are passing or failing using real visitor data.
• AuditCrow - run a free website audit and we'll flag common performance issues - large images, render-blocking scripts, layout instability - with plain-language explanations so you know exactly what to fix.

Common Causes and Quick Fixes

Poor LCP is often caused by:

• Large, uncompressed images - compress them and use modern formats like WebP
• Slow server response time - better hosting or a CDN (Content Delivery Network) can help
• Render-blocking scripts - JavaScript files that prevent the page from displaying until they've fully loaded

Poor INP is often caused by:

• Heavy JavaScript running during interactions - reduce or defer scripts
• Third-party widgets, live chat tools, or tracking scripts that slow the browser's response

Poor CLS is often caused by:

• Images without defined dimensions - always specify width and height so the browser reserves space before the image loads
• Web fonts loading late and causing text to reflow
• Ads or embeds that appear after the main content and push everything down

For a broader list of speed issues to fix, see our post on why website speed matters and our guide on how to audit your website for SEO.

The Takeaway

Core Web Vitals aren't just technical checkboxes - they represent real experiences your visitors are having on your site right now. Improving them helps your rankings, reduces the number of visitors who leave before engaging, and gives everyone who lands on your site a better first impression.

Run a free AuditCrow scan to see what performance issues your site has, or visit our FAQ to learn more about how we analyse your pages.