Why image size impacts website speed
Google's Core Web Vitals — particularly Largest Contentful Paint (LCP) — directly penalise slow-loading images. A page with unoptimised images can take 5–10 seconds to load, devastating your SEO rankings and user experience.
Studies show that 53% of mobile users abandon pages that take longer than 3 seconds to load. Image optimisation is the lowest-hanging fruit for speed improvement.
Recommended image sizes by use case
| Use case | Max width (px) | Target file size | Format |
|---|---|---|---|
| Hero / banner image | 1920 | < 200KB | WebP or AVIF |
| Blog post image | 1200 | < 150KB | WebP or JPEG |
| Thumbnail | 400 | < 30KB | WebP or JPEG |
| Product photo | 800 | < 100KB | WebP |
| Logo | 200–400 | < 20KB | SVG or PNG |
| Icons | 64–128 | < 5KB | SVG |
Format selection: JPEG vs WebP vs AVIF
The format you choose has a massive impact on file size:
- JPEG: Universal support, good compression. Use at 80–85% quality.
- WebP: 25–35% smaller than JPEG at same quality. Supported in all modern browsers. Recommended for most use cases.
- AVIF: 50% smaller than JPEG, but slower to encode and limited support. Best for new projects.
Use PhotoResizer.in's Format Converter to convert images to WebP or AVIF instantly.
For a deep dive, read our WebP vs AVIF comparison.
Quick optimisation checklist
- Resize images to the maximum display size (don't serve 4000px images in a 800px container).
- Compress with lossy compression at 80–85% quality.
- Convert to WebP format for 25–35% additional savings.
- Use lazy loading (
loading="lazy") for below-the-fold images. - Serve responsive images with
srcsetfor different screen sizes. - Use a CDN to serve images from edge locations close to your users.