What Core Web Vitals actually are
Three metrics Google measures on real users visiting your site via Chrome. LCP (Largest Contentful Paint) measures how fast the largest visible element renders. INP (Interaction to Next Paint) measures responsiveness — how quickly the page reacts to clicks and taps. CLS (Cumulative Layout Shift) measures unexpected visual movement. Together they approximate how fast and stable your site feels to a real user on a real device.
Why they matter for SEO
Google uses Core Web Vitals as a ranking factor. Not the biggest one, but when two otherwise-equal pages compete for a search result, the faster one wins. On competitive keywords, Core Web Vitals can be the deciding factor.
What "good" looks like
LCP: under 2.5 seconds (good), under 1.5 seconds (excellent). INP: under 200 milliseconds (good), under 100 milliseconds (excellent). CLS: under 0.1 (good), 0 (excellent).
The top 3 fixes that move the needle
1. Optimise your hero image — serve WebP/AVIF, set explicit width/height attributes, use responsive srcset. 2. Get off slow shared hosting — move to Vercel, Netlify, or a competent VPS with CDN. 3. Remove or defer non-critical JavaScript — especially third-party tracking and chat widgets that load synchronously.
The CLS silent killer: images without dimensions
A staggering number of sites fail CLS because images load without declared width/height. Browsers then shift the layout when images finally appear. Solution: always set dimensions on img tags, or use next/image which handles this automatically.
How to measure correctly
PageSpeed Insights gives you both lab (Lighthouse, deterministic) and field (CrUX, real users) data. Lab data is faster to iterate on; field data is what Google actually uses for ranking. Always check both. If you have Search Console, the Core Web Vitals report there is the ranking-relevant source of truth.
Tools worth using
PageSpeed Insights (free), Chrome DevTools Performance tab, Google Search Console CWV report, web-vitals npm package for real-user monitoring (we ship this on webaccuracy.com via an Analytics integration), and WebPageTest for deep diagnostics.
What does not matter as much as people think
First Contentful Paint (FCP), Time to First Byte (TTFB), and Total Blocking Time (TBT) are diagnostic metrics that feed LCP and INP. Optimising them directly is less important than optimising the outcomes they contribute to.
Frequently asked
- My Lighthouse score is 95 but field data is poor. Why?Lighthouse runs on a simulated fast device. Real users have slower phones and networks. Trust field data (CrUX, Search Console) over lab data for ranking decisions.
- Does Core Web Vitals affect rankings in all countries?Yes, globally, on both mobile and desktop.
- Can I improve CWV without a developer?Partially. Image optimisation and hosting upgrades move the needle without code changes. But hitting excellent CWV usually requires developer work on script loading and layout stability.
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