Google measures your page speed. Your visitors do too. Only one of them tells you.
Core Web Vitals are three measurable performance signals that Google has used as an official ranking factor since 2021. But the story goes well beyond SEO. A slow page costs real money.
What are Core Web Vitals?
LCP (Largest Contentful Paint)
Measures when the largest visible element on the page finishes loading (usually a hero image or heading). Google wants this to happen in under 2.5 seconds.
If a visitor waits three or four seconds to see content, they are often already gone. Bounce rate climbs, conversions drop.
INP (Interaction to Next Paint)
Since March 2024, INP has replaced FID. It measures how fast the page responds to a click, keystroke, or tap. Threshold: under 200 ms.
A page that freezes when you click a button signals unreliability. Shoppers do not forgive that.
CLS (Cumulative Layout Shift)
Measures unexpected layout shifts during loading, like the “Buy” button jumping down right as you tap it. Threshold: under 0.1.
CLS destroys the mobile experience and is the cause of accidental clicks that frustrate visitors.
Why this is also a business issue
Google’s own research shows: when load time increases from 1 to 3 seconds, the probability of a bounce increases by 32%. Shopify found that every 100ms improvement in speed increases conversions by 1%.
In competitive markets, speed is a differentiator.
What typically slows a page down?
Unoptimised images
Images uploaded in their original resolution and format (JPEG, PNG) are the most common cause of poor LCP. Fix: modern formats (WebP, AVIF), correct dimensions, lazy loading for below-the-fold images.
Render-blocking scripts
JavaScript that loads synchronously in <head> halts the browser mid-render. Every analytics pixel, chat widget, and third-party script adds latency.
Too many font requests
Google Fonts loads a single typeface with 2-4 separate network requests. Delays compound. Fix: self-host fonts, use font-display: swap, subset to characters you need.
Missing caching
Without proper cache headers, the browser re-downloads the same assets on every visit. HTTP/2, a CDN, and long max-age directives drastically cut repeat load times.
Slow server response (TTFB)
Time to First Byte reflects your server’s speed. Good hosting and a CDN (like Cloudflare) are the baseline.
How to measure where you stand
- Google PageSpeed Insights is free and shows both lab and field data
- Chrome DevTools → Lighthouse gives a detailed breakdown with actionable advice
- Google Search Console → Core Web Vitals shows real data from your actual visitors
Do not test only from the office on a fast connection. Test on throttled speed (Slow 4G in DevTools) and on mobile, because that is where most of your traffic lives.
What scores should you aim for?
| Metric | Good | Needs improvement | Poor |
|---|---|---|---|
| LCP | < 2.5 s | 2.5 to 4 s | > 4 s |
| INP | < 200 ms | 200 to 500 ms | > 500 ms |
| CLS | < 0.1 | 0.1 to 0.25 | > 0.25 |
The goal is green on all three. Every step toward green shows up in results.
How we approach it
At WebZone we build sites on Astro with Cloudflare infrastructure. Astro ships 0 KB of JavaScript by default and loads only what is truly needed for interactivity. Cloudflare CDN handles global distribution and automatic image compression.
The result is pages that load under 1 second on all devices.
If you are not sure where your site stands, we are happy to take a look. Get in touch and you will have an answer within 24 hours.