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 |
|---|
| 3.97 MB | 247 KB | 94% smaller |
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 WebP is the right target for a PNG
Converting a PNG usually means one of two things: the file is too big for a web page, or a platform will not accept PNG.
WebP solves the first properly. It supports transparency, like PNG, and it compresses like JPG. That combination is what makes it the correct destination — converting to JPG would flatten your transparent background to white.
On the fixed test image used for every measurement on this site, a 3.97 MB PNG became a 247 KB WebP — a reduction of around 94%.
What kind of PNG saves the most?
Photographs. A PNG holding a photograph is a format mismatch to begin with: PNG stores every pixel exactly, and photographs are made of exactly the fine detail that costs the most to store losslessly. Converting one to WebP recovers almost all of that.
Screenshots, logos and diagrams save less, because PNG already handles flat colour and hard edges efficiently. For those, consider optimising the PNG losslessly instead — you keep pixel-perfect text and still get a smaller file.
Lossy or lossless?
This page produces lossy WebP, which is where the large savings come from. At the default quality of 82, photographic content is visually indistinguishable from the source.
For images where every pixel must be exact — a screenshot of code, a diagram with fine hairlines, a logo with crisp edges — lossy compression of any kind is the wrong tool. Keep the PNG.
WebP or AVIF?
AVIF went further on the same test image: 109 KB against WebP’s 247 KB. It also supports transparency.
The trade is encoding speed, which for AVIF is substantially slower, and slightly narrower support outside browsers. If you are converting a handful of hero images, AVIF is worth the wait. If you are converting hundreds, WebP is the practical choice.
Questions
- Does WebP keep PNG transparency?
- Yes. WebP has a full alpha channel, so transparent and semi-transparent areas survive the conversion intact. This is the main reason to choose WebP over JPG when converting a PNG — JPG has no alpha channel and fills transparent areas with white.
- How much smaller will the WebP be?
- For photographic content, dramatically smaller: on the fixed test image here a 3.97 MB PNG became a 247 KB WebP, about 94% smaller. For flat graphics and screenshots the saving is smaller, because PNG already compresses those well.
- Is WebP lossy or lossless?
- Both, depending on the setting. This page uses lossy WebP, which is what makes the large savings possible. If you need a byte-exact copy, keep the PNG and optimise it losslessly instead.
- Will a screenshot look worse as a WebP?
- A little, at the default quality — lossy compression softens hard edges and text. WebP handles this far better than JPG does, but for screenshots where text must stay crisp, optimising the PNG losslessly is the safer option.
- Do all browsers support WebP?
- Every current browser, including Safari since 2020. It is effectively universal on the web now.
- Is my image uploaded?
- No. The decode and encode both run in this browser tab, in a Web Worker. The Uploaded readout measures the page's own outbound traffic, so a successful conversion shows 0 B.
- Is there a file size limit?
- None imposed. There is no upload and no server, so the ceiling is your device's memory.
- Can I convert a folder of PNGs at once?
- Yes. Add as many files as you like — nothing is uploaded, so there is no queue and no per-file cap.
- Should I use WebP or AVIF for PNG images?
- AVIF compresses harder — on the same test image it reached 109 KB against WebP's 247 KB. WebP encodes much faster and is accepted by slightly more software. For images with transparency, both work; WebP is the safer default.
- Will there be a watermark?
- No. Nothing is added to the image and no feature is paywalled.