Core Web Vitals: the three numbers Google cares about

Site speed isn't just a feeling. Google measures it with three metrics — Core Web Vitals — and uses them as a ranking signal. They also decide how many visitors leave before the page has finished loading.

One thing to get straight before the numbers: Google grades these on real visitors, not on your test run. The bar is the 75th percentile, so three out of four page loads have to land in "good" before you pass. A clean score on your own laptop proves nothing.

LCP — Largest Contentful Paint

When the largest element on screen finishes rendering, usually the hero image or the headline. It's the moment a visitor feels "it's here".

• Good: under 2.5 s
• Needs work: 2.5–4 s
• Poor: over 4 s

Most common culprit: uncompressed images and render-blocking JavaScript.

CLS — Cumulative Layout Shift

How much the content jumps around while the page loads. Nothing is more irritating than clicking a button that moved at the last second.

• Good: under 0.1
• Poor: over 0.25

The fix: reserve the dimensions of images and embeds up front (width/height), and never inject content above what has already rendered.

INP — Interaction to Next Paint

How quickly the site answers a click or a tap. It replaced the older FID in 2024 and measures real responsiveness, not just the first interaction.

• Good: under 200 ms
• Poor: over 500 ms

The main cause of a sluggish response: too much JavaScript running on the main thread.

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LCP and CLS can be measured in a lab, and that is where Reconvio gets them — from Lighthouse, translated into concrete findings instead of a table of numbers. INP is the exception. It needs someone to actually click, so no lab tool, Lighthouse included, can hand it to you. That one only comes from real visitors.