Trading a little size for a lot of compatibility
AVIF and WebP are both modern web formats, but they are not equally accepted. WebP has been displayable in every mainstream browser since Safari 14 in 2020 and is understood by most image editors, content systems, chat apps and even some email clients. AVIF arrived in Safari only with version 16.4 in 2023, is still missing from many CMS thumbnailers and image proxies, and needs an extension on Windows. If an AVIF has to go somewhere that might not understand it, WebP is the smallest format that will almost certainly work.
The conversion decodes the AVIF with your browser's own image pipeline, sends the pixels to a Web Worker, and encodes them with libwebp compiled to WebAssembly. Nothing is uploaded, and the encode is fast, typically well under a second for a web-sized image.
The browser must be able to read AVIF
This is the one requirement that can stop the tool cold. There is no built-in AVIF decoder; if your browser cannot display AVIF, the file cannot be converted, and you will see a failure message rather than a bad file. Chrome, Edge and Firefox have all decoded AVIF for years; Safari needs macOS 13 or iOS 16.4 and later. If you are on an older Apple device, that is the reason it fails.
Lossy into lossy, done carefully
Both formats are lossy, so this is a second generation of compression. AVIF tends to smooth texture; WebP smooths too but less aggressively, and adds its own slight blur at low settings. Stacked at sensible values the result is fine; stacked at aggressive values, photos acquire a painted look. The quality control here spans 20 to 95 and starts at 80; for this direction, use 82 to 90. You are converting to gain compatibility, not size, so let the file be a little larger and keep the image faithful to the AVIF you started with.
The alpha channel is preserved, and WebP stores it losslessly, so cut-outs and logos keep their soft edges exactly. Animation is not preserved: an animated AVIF becomes a still WebP of its first frame. Bit depth drops to 8 and colour is normalised to sRGB, so an HDR or wide-gamut AVIF loses that extra range. Metadata and profiles are not written. Pixel dimensions are unchanged.
Typical sizes
Because WebP is the less efficient codec, the file usually grows. Typical, not guaranteed:
- A 1400x900 hero image of 110 KB as AVIF usually becomes 170 to 260 KB as WebP at quality 85.
- A 1000x1000 transparent product cut-out of 45 KB as AVIF typically lands at 80 to 130 KB, the alpha plane accounting for a fair share.
- A 600x400 thumbnail of 18 KB as AVIF often comes out at 28 to 40 KB.
If the image is destined for print or an editor rather than a web page, and transparency or pixel-exact fidelity matters, AVIF to PNG is the safer choice despite the far larger file. If it is destined for a form that only accepts classic formats, AVIF to JPG is the universal answer.
The better pattern for websites
If you are converting because some visitors cannot see your AVIF images, the right fix is usually not to abandon AVIF but to serve both. The HTML picture element lets you list the AVIF first and the WebP second, and each browser picks the best format it understands. Use this page to generate the WebP variants, keep the AVIF files, and add a JPG only if you also need to support very old browsers. The guide WebP vs AVIF vs JPEG covers the support table and shows the size differences on real images.
Limits are the usual ones for an in-browser tool: memory for very large images, one file at a time in a batch, and no HDR, animation or lossless output.