What a plain compress saves
With the defaults on this page, JPEG and WebP files are re-encoded at quality 80 and 78, and PNG files are repacked without changing a pixel. The table shows what that did to six test files.
The photo lost 61% of its weight because its source was saved at a very high quality. A file straight from a phone or a camera app is usually compressed harder already, so expect a smaller saving. The PNG rows show both cases: a PNG written by a plain encoder shrank by about a quarter (25% and 22%), while one that had already been optimised came back at the same size.
| Test image | Original | After | Change | Fidelity (PSNR) | Time |
|---|---|---|---|---|---|
| Photo, JPEG | 694 KB | 274 KB | 61% smaller | 36.2 dB | 578 ms |
| Photo, WebP | 403 KB | 378 KB | 6% smaller | 42.4 dB | 476 ms |
| Screenshot, PNG as exported | 61 KB | 46 KB | 25% smaller | Lossless | 978 ms |
| Screenshot, PNG already optimised | 46 KB | 46 KB | No change | Lossless | 956 ms |
| Illustration, PNG as exported | 121 KB | 94 KB | 22% smaller | Lossless | 1.4 s |
| Illustration, PNG already optimised | 94 KB | 94 KB | No change | Lossless | 1.3 s |
JPEG and WebP are recompressed at quality 80 and 78. PNG stays lossless, so the pixels are identical and only the packing improves; a PNG that was already optimised cannot get smaller. Higher PSNR means closer to the original. Test images are synthetic files made by this project: a 2000 x 1333 landscape photo, a 1600 x 900 interface screenshot and a 1200 x 1200 transparent illustration. Timings: one thread of WebAssembly on Node v22.23.4, Intel(R) Xeon(R) Processor @ 2.10GHz, 2 cores, measured 2026-10-31. Other devices will differ.
Choosing a quality
For photos, quality 75 to 85 is where most people stop seeing a difference. Below about 60, skies and skin start to show blocks and banding. Open the compare view on a result: it gives you a slider and a 100% zoom, which is where compression damage shows up. If you can see it, raise the quality by 5 and run the image again. Running the same image again does not count against the daily limit.
When you need a size, not a quality
If a form rejects anything over 100 KB, pick 100 KB under Max file size. The tool lowers quality until the file fits and shrinks the pixel dimensions only when quality alone cannot get there. It never enlarges a small image. There are ready-made pages for 10 KB, 20 KB, 50 KB, 100 KB, 200 KB, 500 KB and 1 MB.
Metadata and colour
Camera details, GPS location and edit history are removed by default. That saves a little space and keeps your location out of files you share. If colours look flat on a wide-gamut screen afterwards, open Advanced settings and keep the colour profile under Metadata. The metadata page explains each kind of data.
Limits worth knowing
Compressing a JPEG again and again adds loss each time, so start from the original when you have it. WebP and AVIF usually give smaller files than JPEG at a similar look, but not every app opens them. If your destination does, convert to WebP for a bigger saving than recompression gives.
What happens to each format
- JPEG is decoded and saved again with MozJPEG, in progressive form, at the quality you choose.
- WebP is saved again with libwebp at your quality, or losslessly if you switch that on.
- PNG stays lossless. The pixels are packed again by an optimiser, so the picture is identical and the file is usually smaller when the original was not optimised.
- AVIF is saved again with libavif, which is the slowest of the four.
The format is read from the file contents and not from the extension, so a JPEG that was renamed to .png is still handled as a JPEG.
Questions
Does compressing change the dimensions?
No. The pixel size stays the same unless you set a size target or choose a resize option.
Why did my PNG not get smaller?
It was probably optimised already. PNG compression is lossless, so there is a floor. Converting it to WebP is the usual next step.
Will my photos stay upright?
Yes. Photos are rotated to match their orientation before saving, so they do not come out sideways.
Is anything uploaded?
No. The compression runs on your device.