Page speed refers to how quickly a webpage loads and becomes interactive for users. It encompasses multiple metrics — time to first byte (TTFB), time to interactive (TTI), and Google's Core Web Vitals — not a single measurement.
Why page speed matters
For SEO: Google confirmed page speed as a ranking signal in 2010 for desktop, and extended it to mobile in 2018. The 2021 Page Experience update further formalised this through Core Web Vitals as measurable ranking signals.
For conversions: The impact on business outcomes is significant. Research by Google shows that as page load time increases from 1 to 3 seconds, the probability of bounce increases by 32%. A 1-second delay in mobile load time can reduce conversions by up to 20%.
For user experience: Users expect pages to load in under 2–3 seconds. Slow pages signal unreliability, especially in mobile contexts with variable network conditions.
Key page speed metrics
| Metric | What it measures | Good threshold |
|---|---|---|
| TTFB | Time to first byte from server | Under 0.8s |
| LCP | Largest visible element loaded | Under 2.5s |
| TTI | Time until page is interactive | Under 3.8s |
| TBT | Total blocking time | Under 200ms |
| CLS | Layout stability | Under 0.1 |
How to measure page speed
- Google PageSpeed Insights (pagespeed.web.dev) — Shows both lab data (Lighthouse) and real-user field data from the Chrome UX Report
- Google Search Console → Core Web Vitals report — Shows performance across all your indexed pages
- Chrome DevTools → Lighthouse tab — Detailed diagnostics for individual pages
- WebPageTest (webpagetest.org) — Advanced testing with waterfall charts and multi-location testing
The most impactful improvements
Images: Unoptimised images are the single most common cause of slow pages. Use WebP format, compress images, set explicit dimensions, and lazy-load images below the fold.
Render-blocking resources: JavaScript and CSS files that load in the <head> block the browser from rendering the page. Defer non-critical scripts, inline critical CSS, and remove unused code.
Server response time: A slow TTFB (over 0.8s) multiplies every other performance problem. Use a CDN, choose quality hosting, and implement server-side caching.
Third-party scripts: Analytics tags, chat widgets, and social embeds load synchronously by default and can add seconds to load time. Load them asynchronously after the main content.
Related terms
- Core Web Vitals — Google's specific page speed metrics
- Technical SEO — the broader optimisation category
- SEO
