Core Web Vitals: Why Website Speed Matters for Your Business

In 2021, Google began using Core Web Vitals as ranking factors in search results. For business owners, this technical change has practical consequences: website speed now directly affects your visibility in Google. But beyond rankings, these metrics reflect real user experience—and user experience affects whether visitors become customers.

What Are Core Web Vitals?

Core Web Vitals are three specific metrics that Google uses to assess user experience:

Largest Contentful Paint (LCP) measures loading performance—specifically, how long it takes for the largest content element (usually a hero image or heading) to appear. Google considers under 2.5 seconds "good," between 2.5-4 seconds "needs improvement," and over 4 seconds "poor."

Interaction to Next Paint (INP) measures responsiveness—how quickly the page responds when users interact with it. This replaced First Input Delay (FID) in March 2024. Good scores are under 200 milliseconds; poor scores exceed 500 milliseconds.

Cumulative Layout Shift (CLS) measures visual stability—whether elements move around unexpectedly as the page loads. A score under 0.1 is good; above 0.25 is poor. You've experienced bad CLS when you try to click a button and the page shifts, causing you to click something else.

Why These Metrics Matter Beyond SEO

While Google's ranking factors get the headlines, the real importance of these metrics is what they measure: actual user experience. Consider what each metric really represents:

Poor LCP means visitors stare at a loading screen—or worse, a blank page—while your competitors' sites are already engaging them. Every second of waiting increases the chance they'll hit the back button.

Poor INP means your site feels sluggish. When users click a button and nothing seems to happen for half a second, they click again. Or they assume the site is broken and leave. This particularly hurts eCommerce sites where add-to-cart buttons and checkout flows need to feel instantaneous.

Poor CLS is perhaps the most frustrating for users. They're about to click "Add to Cart" and the page shifts, causing them to click an ad instead. Or they're reading content and text jumps around as images load. This erodes trust in your site's professionalism.

Real Business Impact

The connection between site speed and business outcomes is well-documented. Some examples from industry research:

Amazon found that every 100ms of latency cost them 1% in sales.
Pinterest increased search engine traffic by 15% when they reduced perceived wait times by 40%.
BBC found they lost 10% of users for every additional second of load time.

For smaller businesses, the relative impact can be even greater. A local business competing with well-optimised national chains can't afford to give away visitors due to slow performance.

We saw this with Bottle Company South, whose previous website took over 5 seconds to become interactive on mobile. After rebuilding on OpenCart with performance as a priority, load times dropped to under 2 seconds. They reported a significant increase in mobile orders, which they attributed largely to the improved experience.

Common Causes of Poor Scores

Understanding what causes poor Core Web Vitals helps identify what needs fixing:

Poor LCP

Unoptimised images: Large images that could be compressed, or images served at much larger dimensions than displayed.
Slow server response: The server takes too long to send the initial HTML. Common with overloaded shared hosting.
Render-blocking resources: CSS and JavaScript files that prevent the page from rendering until they're downloaded.
Client-side rendering: Sites built with frameworks like React that render everything in the browser rather than on the server.

Poor INP

Heavy JavaScript: Large JavaScript bundles that take a long time to parse and execute.
Long-running tasks: JavaScript operations that block the main thread for extended periods.
Too many event listeners: Excessive handlers attached to page elements.
Inefficient frameworks: Some frontend frameworks add significant overhead to every interaction.

Poor CLS

Images without dimensions: When images don't have width and height attributes, the browser can't reserve space for them.
Ads and embeds: Third-party content that loads after the page and pushes other elements around.
Web fonts: When custom fonts load and replace system fonts with different metrics, text reflows.
Dynamic content: Content inserted above existing content without proper space reservation.

How to Check Your Scores

Several tools can measure your Core Web Vitals:

PageSpeed Insights (pagespeed.web.dev) is Google's official tool. It shows both lab data (simulated tests) and field data (actual user experiences from Chrome users who visit your site).

Google Search Console has a Core Web Vitals report showing how your pages perform for real users over time. This is the data Google actually uses for ranking.

Lighthouse is built into Chrome's DevTools (press F12, then go to the Lighthouse tab). It runs a simulated test on your current page and provides detailed recommendations.

WebPageTest (webpagetest.org) offers detailed waterfall charts showing exactly how your page loads, helpful for diagnosing specific issues.

We recommend checking PageSpeed Insights first—if your scores are green across all three metrics, you're in good shape. If not, the detailed recommendations will point you toward what needs attention.

Improvement Strategies

Improving Core Web Vitals often requires technical changes, but some improvements are straightforward:

Quick Wins

Compress and properly size images. Modern formats like WebP offer significant size reductions.
Add width and height attributes to all images to prevent layout shifts.
Use font-display: swap for web fonts so text remains visible while fonts load.
Defer non-critical JavaScript with async or defer attributes.
Enable caching so returning visitors don't re-download resources.

Larger Changes

Move to faster hosting—often the single biggest improvement available.
Implement server-side rendering if currently using client-side only.
Audit and remove unnecessary plugins and scripts.
Consider a CDN to serve content from servers closer to your visitors.
Rebuild with a performance-focused framework if the current platform can't be adequately optimised.

When Optimisation Isn't Enough

Sometimes a website's architecture simply can't achieve good Core Web Vitals. If you're running an older WordPress site with years of accumulated plugins, or a page builder that generates bloated HTML, optimisation may be a losing battle.

In these cases, a rebuild using modern, performance-focused technology often makes more sense than endless optimisation of a fundamentally slow platform. We've helped several clients through this transition, typically achieving 2-3x performance improvements that wouldn't have been possible with their existing systems.

Getting Help

If your Core Web Vitals scores are hurting your search rankings and user experience, we can help. We start with a thorough audit to understand what's causing poor performance, then recommend the most cost-effective path to improvement—whether that's targeted optimisation or a strategic rebuild.

Request an audit to understand your site's current performance and what it would take to achieve consistently good scores.