Web Performance
Core Web Vitals: why fast websites convert more leads
Speed isn't just a technical metric — it's a conversion lever. We break down LCP, INP and CLS, and how to win on each without bloat.
LCM Engineering· · 6 min read
Speed is a conversion lever, not a vanity score
Every additional second of load time measurably reduces conversions. Fast sites feel trustworthy, keep people engaged, and rank better. Core Web Vitals give you three concrete metrics to optimise — and each maps directly to revenue.
Largest Contentful Paint (LCP)
LCP measures how quickly the main content appears. Aim for under 1.5 seconds. The biggest wins come from optimised, responsive images (AVIF/WebP), preloading the hero image and critical font, and serving static HTML instead of heavy client-side rendering.
Interaction to Next Paint (INP)
INP measures responsiveness to taps and clicks. Heavy JavaScript is the usual culprit. Shipping minimal JS, deferring non-critical scripts and favouring CSS animations over JS libraries keeps interactions instant.
Cumulative Layout Shift (CLS)
CLS measures unexpected movement as the page loads — nothing erodes trust faster than a button that jumps. Reserve space for images and embeds, use font-display swap with sized fallbacks, and avoid injecting content above existing elements.
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