Site speed is no longer an engineering concern — it is a ranking factor and a direct conversion multiplier. Every 100 milliseconds of delay costs e-commerce about 1% of revenue. Here are Google's metrics without the jargon.
The three metrics Google measures
LCP (Largest Contentful Paint) — when the user sees the main content. Target: under 2.5 seconds; our standard is under 1.2. CLS (Cumulative Layout Shift) — how much the layout jumps during load; norm is under 0.1. INP (Interaction to Next Paint) — response delay to actions; under 200 ms.
What kills LCP
- Unoptimized images: WebP/AVIF and correct sizes give up to 60% of the effect
- Fonts without preload: text waits for the font or flashes a fallback
- Third-party scripts in head: every marketing pixel taxes speed
- Client rendering where server rendering belongs
Why we build on Next.js
Server rendering returns ready HTML — the browser does not wait for JavaScript to show content. Static generation makes catalog and blog pages instant. Image optimization and code splitting work out of the box. The median LCP of our projects is 1.1 seconds.
Speed is a process, not a one-off
The performance budget is fixed before design: page weight, script count. CI checks every release — a regression blocks the rollout. Otherwise a fast-at-launch site doubles its weight in a year of pixels.
Check your site in PageSpeed Insights: an LCP above 2.5 seconds costs you rankings and conversion. A performance audit finds the main leaks in a week.