Part of our complete guide to website design & development.
The three metrics
- LCP (Largest Contentful Paint) — how long the main content takes to appear. Good: under 2.5s.
- INP (Interaction to Next Paint) — how quickly the page responds when users interact. Good: under 200ms. (INP replaced FID.)
- CLS (Cumulative Layout Shift) — how much the layout jumps around. Good: under 0.1.
How to fix LCP
- Compress and properly size images; use modern formats (WebP/AVIF).
- Preload the hero image; don’t lazy-load above-the-fold content.
- Enable caching and a CDN; reduce server response time.
- Cut render-blocking CSS/JS.
How to fix INP
- Reduce heavy JavaScript — especially bloated page builders and unused plugins.
- Break up long tasks; defer non-critical scripts.
- Limit third-party tags (chat widgets, trackers) — they’re common culprits.
How to fix CLS
- Set explicit width/height on images and embeds.
- Reserve space for ads, banners and cookie notices.
- Preload fonts and avoid late font swaps.
How to measure
Use PageSpeed Insights and the Core Web Vitals report in Search Console for field data (real users) — lab scores alone can mislead. Test on real mobile devices, not just desktop.
Why it pays
Speed is a ranking factor, but the bigger win is conversion: every second of delay costs you users. It’s why we target green vitals on every build — see our website service and the Launch Checklist.
FAQ
What are Core Web Vitals?
Google’s three UX metrics: LCP (loading, under 2.5s), INP (responsiveness, under 200ms) and CLS (visual stability, under 0.1).
What replaced FID?
INP (Interaction to Next Paint) replaced First Input Delay as the responsiveness metric.
Do Core Web Vitals affect rankings?
Yes – they’re a ranking signal, and they strongly affect conversions, which usually matters more.
How do I fix a slow WordPress site?
Compress images, enable caching/CDN, cut render-blocking and unused JavaScript (page builders and third-party tags are common culprits), and set image dimensions to stop layout shift.