Core Web Vitals are Google's specific performance metrics that measure how fast, stable, and responsive a website feels to real users - and they are a direct ranking factor in Google Search. The three metrics are Largest Contentful Paint (LCP, measuring load speed), Interaction to Next Paint (INP, measuring responsiveness), and Cumulative Layout Shift (CLS, measuring visual stability). UK businesses whose websites fail Core Web Vitals thresholds rank lower than competitors who pass them, all else being equal.
Google has been explicit: your website's performance is a ranking factor. Not just a technical nice-to-have - a direct input into where you appear in search results relative to your competitors.
Core Web Vitals are the specific measurements Google uses. If you have heard the phrase but do not know what it means or what to do about it, this guide explains what matters, why it matters, and what you can actually do about it.
What are Core Web Vitals?
Core Web Vitals are three measurements that Google uses to assess the real-world performance of a web page from the perspective of a user visiting it:
1. Largest Contentful Paint (LCP) How long it takes for the largest visible element on the page to load. Usually the hero image, the main heading, or the largest block of text above the fold.
- Good: under 2.5 seconds
- Needs Improvement: 2.5-4 seconds
- Poor: over 4 seconds
If a user on a 4G connection sees a blank or partially-loaded page for more than 4 seconds, your LCP is poor and Google penalises your ranking for that page.
2. Interaction to Next Paint (INP) How responsive the page is to user interaction. Measures the delay between a user clicking, tapping, or pressing a key, and the browser updating visually in response.
- Good: under 200 milliseconds
- Needs Improvement: 200-500ms
- Poor: over 500ms
If clicking a navigation link or a dropdown causes a noticeable delay before anything happens, your INP is failing.
3. Cumulative Layout Shift (CLS) How much visible content moves unexpectedly as the page loads. A page where buttons, images, or text blocks shift position while the user is trying to click something has high CLS.
- Good: under 0.1
- Needs Improvement: 0.1-0.25
- Poor: over 0.25
If you have ever tried to click a link on a website and clicked the wrong thing because an image or ad loaded and pushed everything down - that is a CLS problem.
Why Core Web Vitals matter for UK small businesses
Google uses Core Web Vitals as a tiebreaker signal for pages with similar content quality. In competitive local markets - "plumber Birmingham", "solicitor Manchester", "restaurant Edinburgh" - the performance difference between two otherwise similar pages can determine who appears in the top three results.
For mobile searchers (over 60% of local search traffic in the UK), the performance stakes are higher. Core Web Vitals on mobile are measured on typical mobile network speeds, not WiFi. A website that performs well on a desktop WiFi connection often performs badly on a 4G mobile connection - and Google measures mobile performance specifically.
Beyond rankings, performance affects conversion directly. Research consistently shows:
- A 1-second delay in load time reduces conversion by 7% (Akamai, 2017 State of Online Retail Performance)
- Pages that load in under 2 seconds convert at twice the rate of pages that take 4+ seconds (Google, Think with Google)
- Mobile users are significantly less tolerant of slow pages than desktop users (Google, mobile benchmark report)
Improving your Core Web Vitals improves both your rankings and your conversion rate simultaneously.
How to check your Core Web Vitals
Google PageSpeed Insights (pagespeed.web.dev)
Free, instant. Provides both a lab score (synthetic test on Google's servers) and field data (real user data if your site has enough traffic). Run it on your homepage and your most important landing pages. Run it specifically on mobile - not just desktop. Many UK business websites score well on desktop but poorly on mobile.
The score (0-100) is a composite:
- 90-100: Good (green)
- 50-89: Needs Improvement (orange)
- 0-49: Poor (red)
Google Search Console
Your Search Console account (if set up) has a Core Web Vitals report under "Experience". This shows real user data - how your pages actually performed for visitors using Chrome. It categorises URLs as Good, Needs Improvement, or Poor, and shows trends over time.
If you do not have Google Search Console set up, do it now. It is free, and it is the most important diagnostic tool available to you for understanding how Google sees your site.
What causes poor Core Web Vitals (and what to fix)
Large uncompressed images (worst LCP offender)
The single most common cause of poor LCP on UK small business websites is uncompressed images. A 4MB JPEG on your homepage takes 4-8 seconds to load on a typical mobile connection. Three of them on your homepage and you are looking at an LCP of 12+ seconds.
Fix: Compress all images to under 200KB for typical web display. Use WebP format (supported by all modern browsers). Serve images at the correct display size rather than loading a 3000px image and scaling it down to 600px. A professional website should do all of this automatically.
JavaScript that blocks rendering (LCP and INP)
Many website builders and plugins load large JavaScript files before the page can display anything. The browser downloads, parses, and executes JavaScript - and the page appears blank until this is done.
Fix: Defer non-critical JavaScript. Load third-party scripts (analytics, chat, cookie consent) after the main page has rendered. Eliminate unused JavaScript from plugins and libraries. This is a developer task - not something you can fix in a website builder.
Slow server response time (LCP)
If your web hosting is slow, every other performance optimisation is limited by that ceiling. A server that takes 2 seconds to respond to a request before sending any content cannot achieve good LCP.
Fix: Use fast hosting on modern infrastructure. UK businesses should use hosting with data centres in the UK or EU for lowest latency to UK users. A Content Delivery Network (CDN) helps serve assets from servers close to the visitor.
Missing image dimensions (CLS)
When images load without explicit width and height attributes in the HTML, the browser cannot reserve space for them. As each image loads, it pushes other content down - causing layout shifts.
Fix: Always specify width and height attributes on images in HTML. A properly built website does this automatically.
Ads, cookie banners, and pop-ups injected above content (CLS)
If a cookie consent banner or ad network injects content at the top of the page after the initial load, it pushes existing content down - causing CLS. Particularly bad for mobile where the banner may take up a significant portion of the screen.
Fix: Reserve space for cookie banners and ads before they load. Use consent management platforms that do not cause layout shifts. Do not inject content above existing content after the initial render.
Heavy third-party scripts (INP)
Chat widgets, marketing automation platforms, A/B testing tools, session recording scripts (Hotjar, FullStory) - each of these adds JavaScript execution that competes with the user's interactions for browser processing time, causing delays in INP.
Fix: Audit every third-party script on your site. Load non-critical scripts asynchronously. Consider whether each script provides enough value to justify its performance cost.
Core Web Vitals by platform
| Platform | Typical mobile PageSpeed | LCP | INP | CLS |
|---|---|---|---|---|
| Wix | 30-55 | Often poor | Variable | Often poor |
| Squarespace | 35-60 | Often poor | Variable | Often poor |
| WordPress + plugins | 40-75 | Variable | Poor | Variable |
| Shopify | 45-75 | Variable | Variable | Variable |
| Custom Next.js | 85-97 | Good | Good | Good |
Template platforms make performance promises they cannot keep because their core architecture includes JavaScript and CSS overhead that cannot be removed, and they process images without aggressive optimisation by default.
A custom-built Next.js website with proper image handling (next/image component), lazy loading, and no unnecessary third-party scripts consistently achieves 90-97/100 on PageSpeed - across all three Core Web Vitals.
What score do you actually need?
A score of 90+ across all three Core Web Vitals is the target for any UK small business website that depends on Google for traffic.
At 90+, you are competing on an equal footing with other well-built sites. The ranking differentiator shifts to content quality, backlinks, and topical authority.
At 70-89, you have room to improve but are not severely penalised unless you are in a very competitive market.
At below 70, your rankings are being directly limited by performance, especially on mobile. In competitive local markets, competitors with better scores are ranking above you on this basis alone.
The difference a rebuild makes
A UK small business website rebuilt from a Squarespace or Wix template to a custom Next.js build typically sees:
- PageSpeed mobile score: 30-55 → 90-97
- LCP: 4-8 seconds → under 2 seconds
- CLS: 0.2-0.4 → near zero
- Organic search impressions: +20-40% within 3 months
- Enquiry rate from search: +15-30% from conversion improvement alone
The performance improvement is measurable in Google Search Console within weeks of launch.
How we build for Core Web Vitals
Every website we build at Octelis is built on Next.js with:
- All images processed through the Next.js image component (automatic WebP conversion, correct sizing, lazy loading)
- Third-party scripts loaded asynchronously or deferred
- Server-side rendering for fast initial page delivery
- UK-based CDN for low latency to UK visitors
- No unnecessary plugins or page-builder overhead
All client sites consistently score 90+ on Google PageSpeed for both mobile and desktop.
See our pricing → | Get a free quote →
Related reading:
- What Every Small Business Website Needs in 2026 - the complete website essentials checklist
- What Is SEO and Why It Matters for UK Small Businesses - the foundation of search visibility
- Wix vs Custom Web Design UK - how PageSpeed differences affect rankings in practice
- Squarespace vs Custom Web Design UK - Squarespace performance analysis
