Core Web Vitals: What They Are and Why They Actually Matter

• By Kiwi Commerce
• 01 Dec, 2025
• Marketing

Core Web Vitals: What They Are and Why They Actually Matter

A functional, lightning-fast website is the gold standard in the eyes of both Google and website visitors. Slow, unresponsive sites frustrate users and reduce conversions, while fast, smooth experiences encourage engagement and loyalty.

To help website owners understand and measure the user experience of webpages, Google introduced Core Web Vitals  three specific metrics that evaluate a site’s loading performance, interactivity, and visual stability. In this guide, we’ll explain what these metrics are, how to measure them, and how to optimise your site for better performance, user experience, and search rankings.

Whether your website is built on Magento, Shopify, or any other platform, improving Core Web Vitals is essential for boosting visibility, customer satisfaction, and overall site effectiveness.

Core Web Vitals are a set of metrics that Google uses to evaluate the quality of a user’s experience on a website. These metrics are part of Google’s Page Experience signals and are graded on a scale of Good, Needs Improvement, or Poor.

The three main metrics are:

1. Largest Contentful Paint (LCP) – Loading

LCP measures how quickly the largest visible elements on a page load, such as a hero image, main video, or logo. A fast LCP ensures users can engage with your content immediately.

• Ideal score: 2.5 seconds or less
• Poor score: Longer than 4 seconds

A slow LCP frustrates users and increases the likelihood of them leaving your site prematurely.

2. Interaction to Next Paint (INP) – Interactivity

INP measures how quickly a page responds to user interactions, such as button clicks, link taps, or form inputs.

• Ideal score: 100 milliseconds or less

This metric replaced First Input Delay (FID) in May 2023, as it provides a more accurate reflection of a site’s responsiveness. A low INP improves user satisfaction and encourages continued engagement.

3.Cumulative Layout Shift (CLS) – Visual Stability

CLS evaluates how much content shifts on a page while it is loading.

• Ideal score: 0.1 or less

High CLS can frustrate users, particularly if buttons or links move unexpectedly, leading to accidental clicks and a poor overall experience.

Google prioritises pleasant web experiences for readers,” says an industry expert. “Load times are one of the key ranking factors. We’ve seen significant rank improvements for clients once Core Web Vitals are optimised.

Aside from SEO benefits, optimising Core Web Vitals also provides:

• Higher Rankings on SERPs – Fast, stable sites rank higher and attract more organic traffic.
• More Conversions – A functional, trustworthy website encourages purchases, sign-ups, and other desired actions.
• Better User Retention & Lower Bounce Rates – Fast-loading, responsive sites keep users engaged and reduce frustration.

You can measure Core Web Vitals using several tools:

• Google Search Console (GSC) – Provides an overview of URLs rated Good, Needs Improvement, or Poor.
• PageSpeed Insights – Offers both lab data (simulated) and field data (real user experiences) with recommendations for improvements.
• Lighthouse – Detailed performance auditing tool built into Chrome Developer Tools.
• Chrome User Experience Report (CrUX) – Real-world performance data from users visiting your site.
• Chrome Web Vitals Extension – Measures Vitals in real-time as you browse.

Remember to check both lab (simulated) and field (actual user) data for a complete picture of your website’s performance.

Improving LCP

• Optimise images and videos: Compress, serve modern formats, and prioritise loading for above-the-fold content.
• Use lazy loading: Delay non-essential content until needed, but ensure LCP elements load first.
• Improve server response time: Upgrade hosting, enable caching, use a CDN, and optimise server-side code.

Improving INP

• Reduce JavaScript execution time: Code splitting, minification, and removal of unused scripts.
• Minimise main-thread work: Optimise third-party scripts, use web workers, server-side rendering, and efficient animations.

Improving CLS

• Set size attributes for images and videos: Prevent layout shifts by reserving space.
• Use CSS transforms for animations: Avoid layout-reflow animations.
• Avoid intrusive ads or embeds: Elements that shift content as they load should be managed carefully.

While not officially part of Core Web Vitals, these metrics are worth tracking:

• Time to First Byte (TTFB) – How quickly the server responds to a request.
• First Contentful Paint (FCP) – When the first piece of content is visible.
• Total Blocking Time (TBT) – How long the page is unresponsive due to scripts.
• Time to Interactive (TTI) – How long before the page becomes fully interactive.

Core Web Vitals are part of Google’s broader Page Experience signals, which also include:

• Mobile-friendliness – Ensures your site functions well on mobile devices.
• Safe browsing – Checks for malware or phishing.
• HTTPS security – Protects user data with secure connections.

No Intrusive Interstitials (NII) – Avoids disruptive pop-ups covering main content

Optimising Core Web Vitals is essential for both user experience and SEO success. By understanding LCP, INP, and CLS, measuring your website’s performance, and implementing the right improvements, you can:

• Improve engagement and retention
• Increase conversion rates
• Boost your search engine rankings

Think of your website’s Core Web Vitals like your health check-up regularly monitor them, diagnose issues, and implement fixes to keep your site performing at its best.

A fast, responsive, and stable website isn’t just a technical requirement  it’s a competitive advantage in today’s digital landscape. Kiwi Commerce can help optimise your website and fix these crucial performance issues to improve speed, stability, and overall traffic.