Google WebP Compression Study: WebP is 25-34% smaller than JPEG at equivalent SSIM (avg ~30%)

Claim: Per Google's WebP Compression Study (updated August 7, 2025), WebP is 25-34% smaller than JPEG at equivalent SSIM index. Google's own FAQ summarises this as "an average of 30% more compression than JPEG."

Source: https://developers.google.com/speed/webp/docs/webp_study

Confidence: Verified (Google primary).

Practical implication: Modern image formats (WebP, AVIF) are the lowest-effort, highest-yield CWV improvement available. AVIF is even better than WebP for some image classes (20-50% smaller than JPEG depending on content). Use <picture> with AVIF + WebP + JPEG fallback for broad browser support.