Forms, portals and mailboxes often refuse images above a fixed size. Getting under the limit is the easy part: any compressor can do it. The real question is what is left of the picture. We measured it.
What each limit leaves of a photo
On 23 September 2026 we ran 20 ordinary photos — 3 to 30 megapixels, 1.1 to 8.9 MB — through our compressor at four targets. All 80 results came out under their limit. Long side in pixels (smallest / median / largest), megapixels at the median and the JPEG quality the tool chose:
| Target | Long side, px | Megapixels | Quality |
|---|---|---|---|
| 20 KB | 294 / 450 / 840 | 0.13 | 0.60–0.78 |
| 50 KB | 542 / 813 / 1680 | 0.44 | 0.60–0.75 |
| 100 KB | 854 / 1303 / 2400 | 1.03 | 0.60–0.72 |
| 200 KB | 1356 / 1913 / 4000 | 2.54 | 0.60–0.75 |
So 100 KB is roughly a 1303-pixel picture: most of a laptop screen's width, clean at normal viewing size. 50 KB is a phone-screen picture; 20 KB is a thumbnail.
Two ways to meet a limit — and why one of them ruins the photo
A file size can be reached by keeping every pixel and lowering the JPEG quality, or by keeping the quality and using fewer pixels. The first gives blocks, smeared edges and color blotches; the second, a smaller but clean picture.
The same measurement showed that our compressor used to do the first: at 100 KB it kept the full resolution at a median quality of 0.08, and all 20 photos came out below 0.3. We changed it that day. It now looks for the largest size that fits at quality 0.6 or higher and only goes lower for a picture so detailed that nothing else fits. If you need every pixel, untick "Reduce resolution if needed to reach the target size" — then only the quality goes down.
How to do it
- Open Compress to 100 KB — the target is already set — or the compressor in Target size mode.
- Add your photo, or up to 20 at once.
- Press Compress and download. It takes about a second per photo and happens in your browser: the file is not uploaded anywhere.
Tips that change the result
- Crop first. Every kilobyte is spent on pixels. A scan with a wide border or a photo with a lot of empty background spends the budget on nothing; crop to what matters and the same 100 KB buys a sharper picture.
- Check a document at 100%. For a scan with small print, zoom in before sending. If the text is hard to read, a larger target or a tighter crop helps more than anything else.
- Aim a little below the limit. The tool counts 1 KB as 1,024 bytes, as Windows does; some forms count 1,000. If a form rejects a file right at the limit, set 95 instead of 100.
- Other limits: 20 KB, 50 KB, 200 KB.