Website Speed: Why It's the #1 Factor for Conversions and SEO

Website speed isn't a technical detail. It directly determines how many visitors become customers and where you rank in Google. This article explains why, how it's measured, and what you can do about it.

Why speed affects sales

Google's research shows: each second of additional load time reduces conversions by 7-20%. A site that loads in 1 second converts 3x better than a site that loads in 5 seconds.

For e-commerce, the effect is even stronger. Amazon calculated that every 100ms of delay costs 1% in sales.

Why speed affects SEO

Since 2021, Google has used Page Experience as a ranking factor. Since 2024, Core Web Vitals have been officially in the algorithm. Sites that don't meet these metrics rank lower with all else equal.

Core Web Vitals — the metrics that matter

Largest Contentful Paint (LCP)

The time it takes for the largest visible element to load. Target: under 2.5 seconds. Typically this is a hero image or headline at the top of the page.

Interaction to Next Paint (INP)

How quickly the page responds to a user action — click, tap, input. Target: under 200ms. Replaces the older First Input Delay metric.

Cumulative Layout Shift (CLS)

How much the layout shifts during loading. Target: under 0.1. Bad CLS usually comes from images without dimensions or late-loading elements.

Common causes of slow sites

• Unoptimized images — the most common cause. Photos at 5 MB instead of 200 KB.
• Too many plugins — especially on WordPress.
• Heavy themes and templates with unused features.
• No caching — every visitor generates the page from scratch.
• Weak hosting — €5/month shared plans can't deliver fast responses.
• External scripts — chat widgets, analytics, pixels that block rendering.
• JavaScript bundles without code splitting — clients download the entire codebase, even for pages they don't open.

Optimization steps

1. Start with measurement — PageSpeed Insights and Lighthouse give clear numbers and recommendations.
2. Optimize images — WebP format, lazy loading, correct sizes per screen.
3. Implement caching — at CMS, CDN, and browser levels.
4. Move to quality hosting or CDN — Cloudflare Pages, Vercel, Netlify give an A out of the box.
5. Audit external scripts — remove unnecessary ones, load the rest async or defer.
6. Reduce JavaScript bundle — code splitting, tree shaking, removing unused dependencies.
7. Re-evaluate the theme — a modern, lightweight theme can outperform 20 optimized plugins.

How much speed optimization costs

Basic optimization of an existing site (images, cache, basic settings): €500-€1,500. More serious work (code review, plugin reduction, custom hosting setup): €1,500-€5,000.

When problems are architectural (old theme, heavy platform, unoptimized code), partial optimization gives partial results. In those cases, a full rebuild is often the more reasonable investment.

Conclusion

Speed isn't a luxury. It's the minimum requirement without which other investments in marketing and content have limited effect. A site that loads in under 2 seconds returns better ROI on every euro spent on ads or SEO.