Images typically account for 50–70% of a web page's total size. Optimising images is the single most effective way to speed up a website — often reducing page load time by 2–5 seconds with no change to the visual design.
How Images Slow Down Websites
- Serving 4000px images that display at 800px — 25× more pixels than needed
- Using PNG for photographs — 3–5× larger than equivalent JPG
- Not compressing images before upload — serving files 5–10× larger than necessary
- Not using modern formats like WebP — 30–40% larger than necessary
- Loading all images at page load instead of lazy loading below-fold images
Image Optimisation Checklist for Website Speed
- Resize to display dimensions: Never serve images larger than their display size
- Choose the right format: JPG for photos, PNG for graphics, WebP for both
- Compress: JPG at 80–85% quality or lossless PNG compression
- Convert to WebP: Use imgresizr.com to convert all images to WebP
- Enable lazy loading: Add loading="lazy" to all below-fold images
- Use a CDN: Serve images from geographically distributed servers
Speed Impact by Optimisation Type
| Action | Speed Improvement |
|---|---|
| Resize oversized images | Very high |
| Compress images | High |
| Convert to WebP | High |
| Lazy loading | Medium–High |
| CDN delivery | Medium |
Optimise all website images for free at imgresizr.com — resize, convert to WebP, and compress in seconds.