Website speed test: Core Web Vitals, explained
Measure your site the way Google does: PageSpeed lab data plus real-visitor field data (CrUX). See your LCP, INP and CLS, and the specific changes that will move them.
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Google PageSpeed Insights reports two things. Lab data is a single test in a controlled environment: repeatable, but it can swing between runs. Field data (the Chrome UX Report, or CrUX) is what real visitors experienced over the last 28 days: stable and much closer to what Google uses for ranking.
eighty blends both. Where field data exists we lean on it, so your speed score does not jump around every time you scan. That is a fairer, more honest number than lab-only tools.
Core Web Vitals: LCP, INP and CLS
| Metric | What it measures | Good |
|---|---|---|
| LCP (Largest Contentful Paint) | How fast the main content appears. | under 2.5 s |
| INP (Interaction to Next Paint) | How fast the page responds to clicks and taps. | under 200 ms |
| CLS (Cumulative Layout Shift) | How much the layout jumps while loading. | under 0.1 |
These three are the Core Web Vitals Google uses as a page-experience signal. Pass all three and you remove a real ranking handicap.
Why speed quietly costs you customers
Every extra second of load time raises the chance a visitor leaves before they see anything. On mobile, where most traffic now comes from, slow pages bounce hardest. Faster sites get more pages viewed, more form fills and more sales from the exact same traffic. Speed is not a vanity metric, it is conversion.
How to make your site faster
- Images: serve modern formats (WebP/AVIF), size them correctly, and lazy-load below the fold. Usually the biggest LCP win.
- JavaScript: remove unused scripts and defer the rest. Heavy JS is the usual cause of poor INP.
- Fonts: preload key fonts and use
font-display: swapto avoid invisible text. - Caching and CDN: cache static assets and serve them close to your visitors.
- Reserve space: set width and height on images and embeds to stop layout shift (CLS).
PageSpeed Insights vs eighty
PageSpeed Insights is the gold standard for the speed number itself. eighty runs the same Google engine, then puts your speed next to your security, SEO and AI visibility, and turns it into a prioritised plan: fix this first, because it costs you the most.
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