Why performance matters
Users leave when pages feel slow. Google ranks fast pages higher and conversion drops measurably past 3s LCP.
The three metrics
- LCP (Largest Contentful Paint) — when the biggest above-the-fold element renders. Target ≤ 2.5s.
- CLS (Cumulative Layout Shift) — how much content jumps after first paint. Target ≤ 0.1.
- INP (Interaction to Next Paint) — responsiveness to taps/clicks. Target ≤ 200ms.
Where to measure
Lab data: Lighthouse, WebPageTest. Field data: CrUX (real users), Search Console Core Web Vitals report.