Short answer
Use AVIF if your priority is the smallest possible file — it is typically 20–30% smaller than WebP at the same visual quality. Use WebP if you need guaranteed support in every browser your visitors might use, or if encoding speed matters. Serving AVIF with a WebP fallback gets you both.
WebP vs AVIF, side by side
| Aspect | WebP | AVIF |
|---|---|---|
| File size at equal quality | 25–35% smaller than JPEG | 20–30% smaller than WebP |
| Browser support | Universal in current browsers | All current browsers; absent in older versions |
| Encoding speed | Fast | Noticeably slower — seconds per image |
| Transparency (alpha) | Yes | Yes |
| Animation | Yes | Yes |
| HDR / wide colour | No | Yes |
| Quality at very low bitrates | Blocky artefacts appear | Degrades far more gracefully |
Where the size difference comes from
AVIF is derived from the AV1 video codec, and it inherits AV1's far more sophisticated prediction and transform stages. In practice that means it can describe the same image with less data than WebP, which is built on the older VP8 intra-frame coding.
The gap is largest on photographic content with smooth gradients — skies, skin, shadows — where WebP tends to band and AVIF holds together. On flat graphics, screenshots and logos the two are much closer, and PNG may still beat both.
The encoding-speed trade-off
AVIF encoding is genuinely slow — often several seconds for a large photo where WebP takes a fraction of one. For a static site built once, that cost is paid at build time and does not matter. For images generated on demand, or for a user converting a batch in the browser, it is very noticeable.
Decoding is a different story: AVIF decodes fast enough that visitors will not perceive a difference. The cost is paid by whoever creates the file, not whoever views it.
Comparing them properly
Most comparisons set both formats to "quality 80" and compare the resulting file sizes. That comparison is meaningless, because the quality scale is defined independently by each codec — WebP at 80 and AVIF at 80 are not the same visual quality, so the file sizes are not comparable.
The correct method is to encode each format repeatedly, measure the result against the original with a perceptual metric such as SSIM, and only compare sizes once both formats have reached the same measured quality. That is what our Image Converter does, which is why its numbers differ from the ones you will see quoted elsewhere.
Frequently Asked Questions
Should I switch my whole website to AVIF?
Serve AVIF first with a WebP fallback, using a <picture> element. That gives smaller files to browsers that support AVIF without breaking anything for those that do not. Converting everything to AVIF with no fallback is the only genuinely risky option.
Is AVIF better than JPEG?
Substantially — often half the file size at the same visual quality, plus transparency and HDR that JPEG cannot do at all. The reasons to still use JPEG are compatibility with old software and encoding speed, not quality.
Does converting to AVIF lose quality?
Both are lossy formats, so a conversion always discards some information. Converting an already-compressed JPEG to AVIF compounds two rounds of loss. Convert from the highest-quality original you have rather than from a file that has already been through a lossy encoder.
Which is better for logos and screenshots?
Often neither — PNG is lossless and frequently smaller for flat graphics with few colours and hard edges. Lossy formats spend their bitrate on detail that a screenshot does not have, and their artefacts are most visible exactly where flat graphics have sharp edges.
Try it yourself
Terms used here
- WebP
- AVIF — AV1 Image File Format
- SSIM — Structural Similarity Index Measure
- Lossy vs lossless
Related comparisons
- JPG vs PNG — JPG for photographs. PNG for screenshots, logos and anything needing transparency.
- Compressing vs Resizing an Image — Resize first, then compress. Resizing does far more for file size.