Site speed case study: from three seconds to sub‑one
Introduction. In today’s digital marketplace page load time is a silent revenue driver. A 3 second delay can cost a site up to 7% in conversion, while a sub‑one second experience boosts engagement and rankings. This article walks through a real‑world transformation: how one ecommerce brand shaved 2 seconds from its main landing page without sacrificing features or design. Readers will see the exact tools, measurements, and tactics that made the jump possible, and they can apply the same steps to their own sites.
Baseline assessment and goal setting
The first step is to know where you stand. The client’s existing page averaged 3.1 seconds in Google PageSpeed Insights, with a Lighthouse score of 58/100. They set an ambitious but realistic target: load under one second on a standard broadband connection while keeping the same product catalog and checkout flow.
- Run a full audit with Chrome DevTools, Lighthouse, and real‑user monitoring to capture baseline metrics.
- Identify high‑impact assets—images, third‑party scripts, CSS—and quantify their contribution to render time.
Optimization roadmap: assets, code, and infrastructure
The strategy combined three core pillars. First, asset compression: every image was converted to WebP or AVIF, and lazy loading was enabled for off‑screen images. Second, critical CSS extraction removed 70% of render‑blocking styles, while a service worker cached static assets for instant repeat visits. Third, server‑side improvements—moving from shared hosting to an edge CDN and enabling HTTP/2 multiplexing—cut the initial TCP handshake time by half.
| Item | What it is | Why it matters |
|---|---|---|
| Image compression | WebP/AVIF conversion and lazy loading | Reduces payload by up to 60% |
| Critical CSS extraction | Inline only styles needed for above‑the‑fold content | Eliminates render blocking, speeds first paint |
| Edge CDN + HTTP/2 | Distributes assets closer to users and multiplexes requests | Lowers latency and improves concurrent loading |
Hands‑on workflow: from audit to launch
Day one began with a Lighthouse run. The developer flagged three critical issues: large image, unused CSS, and a blocking third‑party script. Using the Chrome DevTools Performance panel, they replaced the JPEG with an AVIF at 80% quality, removed the unused stylesheet from the build pipeline, and swapped the legacy analytics script for a data‑layer approach that loads asynchronously. After each tweak, they reran Lighthouse to confirm incremental gains.
Common pitfalls and how to sidestep them
A frequent mistake is over‑optimizing without monitoring user experience; compressing images too aggressively can degrade visual quality. Another trap is neglecting mobile performance—many sites hit the target on desktop but lag on 3G networks. Finally, relying solely on automated tools ignores real‑user metrics; always pair audit results with RUM data to validate improvements.
Conclusion. By methodically auditing assets, refactoring critical resources, and upgrading infrastructure, the client achieved a sub‑one second load time—cutting conversion loss by an estimated 7% and boosting SEO rankings. The same principles apply regardless of site size: start with a clear baseline, target high‑impact fixes, validate with real data, and iterate. Your next step? Run a Lighthouse audit on your own landing page, identify the top three bottlenecks, and begin the optimization cycle today.
Image by: ThisIsEngineering
