Why image weight matters for SEO
Images are usually the heaviest part of a web page, and the hero image is very often the element that defines Largest Contentful Paint (LCP), one of Google’s Core Web Vitals. Heavy images slow LCP down, especially on mobile connections, and slow pages tend to lose both rankings and conversions.
Switching to WebP is one of the simplest page speed wins available. It cuts file size without changing how a page looks, and it does not need any new design or development work.
WebP vs JPEG vs PNG
| Format | Best for | Notes |
|---|---|---|
| JPEG | Photographs | Universally supported, but larger than WebP at the same quality. |
| PNG | Graphics needing transparency or sharp edges | Lossless and often very heavy for photos. |
| WebP | Photos and graphics | Supports transparency and both lossy and lossless compression, typically much smaller. |
Getting the most from WebP
- Resize before converting. A 4000px photo displayed at 800px wastes bandwidth whatever its format.
- Set width and height attributes on images to prevent layout shift.
- Lazy-load below-the-fold images with
loading="lazy", but never the LCP hero image. - Keep descriptive file names and alt text when you swap formats, because both help image search.
- Optimise vector graphics too with the SVG Optimiser.