What it actually produces
Measured, not estimated. A procedurally generated 2400×1600 (3.8 MP) test image built to carry photographic entropy: value noise across nine octaves down to near-pixel scale, a dense field of small high-contrast features, a smooth gradient, hard edges and light grain. It is not a photograph — it is reproducible, which a photograph is not. Each figure below comes from running that image through this page.
| Input | Output | Change |
|---|
| 109 KB | 198 KB | 82% larger |
Your own files will differ — a photograph, a screenshot and a diagram compress very differently. The point of a fixed image is that the formats can be compared with each other, not that your result will match.
Why go from AVIF to WebP?
It looks backwards — WebP is the larger format — but the reason is support.
WebP has been in every major browser since Safari added it in 2020, and it is accepted by noticeably more software outside the browser than AVIF, which only reached Safari in 2022. If your audience includes older devices, or your publishing pipeline chokes on AVIF, WebP is the pragmatic choice.
The cost is measurable: on the fixed test image used throughout this site, a 109 KB AVIF became a 198 KB WebP, about 82% larger. Still far smaller than the JPG equivalent at 314 KB.
Convert from the original where you can
This is a lossy-to-lossy conversion. The AVIF already discarded detail, and re-encoding as WebP discards a little more — while spending bits faithfully reproducing AVIF’s own artefacts.
If the original PNG or JPG still exists, convert that instead. The result is both cleaner and, usually, no larger.
Both keep transparency
AVIF and WebP each support a full alpha channel, including semi-transparent pixels, so cut-out product images and soft-edged logos survive the conversion in either direction.
The better answer is usually both
Rather than replacing one with the other, serve both and let the browser decide:
<picture>
<source srcset="photo.avif" type="image/avif" />
<source srcset="photo.webp" type="image/webp" />
<img src="photo.jpg" alt="…" />
</picture>
Current browsers take the smallest file, older ones fall back gracefully, and nothing has to be decided in advance.
Questions
- Why would I convert AVIF to WebP if AVIF is smaller?
- For support. WebP has been in every major browser since 2020 and is accepted by noticeably more non-browser software than AVIF, which only reached Safari in 2022. If your audience or toolchain includes older systems, WebP is the safer format even though the file is larger.
- How much bigger will the WebP be?
- On the fixed test image used here, a 109 KB AVIF became a 198 KB WebP — around 82% larger. That is the size cost of the broader compatibility.
- Is transparency preserved?
- Yes. Both formats support a full alpha channel, including semi-transparent pixels.
- Does this conversion lose quality?
- Some. It is a lossy-to-lossy conversion, so a little more detail goes each time. If you still have the original PNG or JPG, converting that directly to WebP gives a better result.
- Is WebP or AVIF better?
- AVIF compresses harder; WebP encodes far faster and is supported more widely outside browsers. Neither is universally better. Serving both from a picture element, with the browser choosing, avoids the question entirely.
- Is my image uploaded?
- No. Decoding and encoding run in this browser tab. The Uploaded readout beside the result measures the page's own outbound traffic, so a successful conversion reads 0 B.
- Is there a file size limit?
- None imposed. Your device's memory is the only ceiling.
- Can I convert in bulk?
- Yes, and this is one of the faster conversions here — WebP encoding is quick, so large batches finish in reasonable time.
- Will there be a watermark?
- No. Nothing is added and no feature is paywalled.
- What should I use for images people will download?
- JPG. Both AVIF and WebP are web formats, and both are still rejected by a long tail of desktop software, print services and upload forms.