Convert images to WebP or AVIF
Modern image formats are 25–50% smaller than JPEG/PNG at the same visual quality.
What it means
JPEG and PNG date from the 1990s. WebP and AVIF are modern formats that all current browsers support, producing dramatically smaller files for the same picture.
Why it matters
Images are usually the heaviest thing on a page. Cutting their size in half is the single cheapest speed win available — and it directly improves LCP and your mobile score.
How to fix it
- Export new images as WebP (or AVIF for even smaller files) directly from your design tool, or batch-convert existing ones with Squoosh or ImageMagick.
- On WordPress, install an optimisation plugin (ShortPixel, Imagify, or Smush) that converts automatically.
- Use the <picture> tag to serve the modern format with the old one as fallback for very old browsers.
- While you're at it, resize images to their display size — a 4000px-wide photo in a 400px slot wastes 90% of its bytes.
Helpful tools
- Squoosh
- TinyPNG
- ShortPixel / Imagify (WordPress)
Not sure if this affects your site? Analyze your website for free or compare it with a competitor.
Related guides
- Fix slow Largest Contentful Paint (LCP): Make the biggest visible element on your page load in under 2.5 seconds.
- Stop layout shifting (CLS): Reserve space for images and embeds so the page stops jumping while loading.
- Reduce Total Blocking Time (TBT): Break up long JavaScript tasks so the page stays responsive to taps and clicks.
- Improve mobile page performance: Cut image weight, JavaScript, and server lag so the page loads fast on phones.