Site speed optimisation is the technical practice of reducing the time it takes for web pages to load and become interactive for users. It encompasses image compression, JavaScript and CSS minification, caching strategies, CDN implementation, server response time reduction, and eliminating render-blocking resources. Google uses site speed as a ranking factor through Core Web Vitals (LCP, INP, CLS) — making speed optimisation both a user experience imperative and an SEO requirement. Slow sites also convert at lower rates, so speed improvements have direct commercial as well as SEO benefits.
Site speed is one of the most impactful technical SEO improvements available, yet many businesses accept slow sites as inevitable. In reality, the most common speed problems — oversized images, too many HTTP requests, unoptimised JavaScript, and poor hosting — are solvable with specific, targeted interventions that can dramatically improve loading time without requiring a full site rebuild.
The highest-impact site speed improvements
- Image optimisation — convert to WebP/AVIF, resize to display dimensions, compress without visible quality loss; often saves 50-80% of image file size
- Enable browser caching — serve CSS, JavaScript, and images with long cache TTLs (1 year for versioned assets)
- Implement a CDN — serve static assets from servers geographically closer to users; reduces latency globally
- Minify CSS, JavaScript, and HTML — remove whitespace and comments from code files; reduces file sizes by 10-30%
- Defer non-critical JavaScript — load analytics, chatbots, and marketing scripts after initial page render
- Optimise server response time — upgrade hosting if TTFB exceeds 600ms; consider managed hosting for WordPress sites
- Reduce DOM complexity — excessive HTML elements slow rendering; keep DOM nodes under 1,500
- Preload critical resources — use <link rel='preload'> for fonts, hero images, and critical CSS
Core Web Vitals (which are primarily speed metrics) are confirmed Google ranking factors — pages passing all three CWV thresholds (LCP, INP, CLS) receive a ranking advantage over failing pages. The magnitude of this advantage varies by keyword competitiveness: in very competitive markets where all other factors are equal, CWV performance can be a meaningful tiebreaker. Speed also has indirect ranking effects through engagement metrics — faster pages have lower bounce rates and higher session quality, which Google uses as quality signals.
TTFB (Time to First Byte) is the time between a browser sending a request to a server and receiving the first byte of the response — essentially, how fast the server responds. A slow TTFB (over 600ms) delays everything else: no rendering can begin until the first byte arrives. TTFB is affected by server performance, hosting location, database query speed, and server-side code efficiency. Improving TTFB through better hosting, database optimisation, or server-side caching has a multiplier effect — it improves all subsequent loading metrics simultaneously.