Core Web Vitals, explained for decision-makers
Three numbers describe how fast your site feels to real visitors. Here's what they mean and why they matter.
Trillune Engineering5 min read
Core Web Vitals are Google's metrics for real-world user experience. They're measured from actual visitors' browsers, which makes them more honest than a single lab test on a fast laptop.
The three metrics
- Largest Contentful Paint (LCP) — how long until the main content is visible. 'Good' is 2.5 seconds or less.
- Interaction to Next Paint (INP) — how quickly the page responds when someone taps or clicks. 'Good' is 200 milliseconds or less.
- Cumulative Layout Shift (CLS) — how much the layout jumps around while loading. 'Good' is 0.1 or less.
Google assesses these at the 75th percentile of page visits, so a site needs to be fast for most visitors — including those on mid-range phones and patchy connections — not just on average.
Why they matter commercially
Slow, jumpy pages make visitors hesitate at exactly the moments you want them to act: product pages, checkout, sign-up. Page experience is also one of many signals considered in search. The strongest reason to care, though, is simply that fast sites are nicer to use.