File size: the 25–35% rule
Google's original WebP study compared 1 million images from the web and found WebP files were 25–34% smaller than JPEGs at equivalent SSIM (structural similarity) scores. Independent tests since then land in the same range. On a page with 1.5 MB of JPEGs, that is roughly 450 KB saved for every visitor, or several seconds on a 3G connection.
Where the savings come from
JPEG splits the image into 8×8 blocks and compresses each independently. WebP, derived from the VP8 video codec, predicts each block from its already-coded neighbours and only stores the difference. It also uses a smarter entropy coder and a deblocking filter that hides compression seams. The result: fewer bytes for the same picture and fewer visible artifacts at low quality.
Image quality
At high quality settings (85+), the two formats are visually indistinguishable; WebP is simply smaller. At aggressive settings (50–70), WebP holds up noticeably better: gradients stay smooth, skies don't band, and edges don't develop JPEG's characteristic 'mosquito noise'. WebP can look slightly softer at very low quality because of its in-loop filtering, which most viewers prefer to blockiness.
Features JPEG never had
- Transparency: WebP carries an 8-bit alpha channel, so product cut-outs and logos no longer need PNG.
- Animation: animated WebP replaces GIF at a fraction of the size.
- Lossless mode: WebP lossless is about 26% smaller than PNG.
- Metadata: both support EXIF, XMP and ICC profiles (browser converters typically strip EXIF).
Browser and platform support
WebP has been in Chrome since 2010, Firefox and Edge since 2019, and Safari since macOS Big Sur / iOS 14 in 2020. Per Can I use(opens in new tab), global support exceeds 97%. WordPress accepts WebP uploads natively since 5.8, Shopify, Squarespace, Wix and Webflow all serve it. The only relevant holdouts are Internet Explorer and some email clients, both of which are best handled with a JPEG fallback.
Serving JPEG as a fallback
Use the HTML <picture> element: list the WebP <source> first and a JPEG <img> last. Browsers pick the first format they understand. Most CDNs and image plugins do this automatically.
SEO and Core Web Vitals
Lighthouse and PageSpeed Insights flag JPEG images under the audit 'Serve images in next-gen formats' and estimate the savings from WebP. Because hero images are almost always the Largest Contentful Paint element, switching them to WebP is often the single biggest LCP improvement available. Better LCP means a better page experience signal in Google Search.