Compress a PDF to under 300 KB
Bring a PDF under 300 KB without an account or a watermark. Every encode attempt happens in this tab, so the file never leaves your computer.
- Runs in your browser
- Files are never uploaded
- Free, no account
The comfortable middle
300 KB is where a multi-page document stops being a compromise. It is roughly 50 KB a page across six pages — enough for a scan at around 110 DPI at a JPEG quality that does not show blocking, which is the point where most people stop being able to tell that anything happened to the file.
It shows up as a limit on contract-submission portals, on some medical-records upload forms, on grant applications, and as a self-imposed target for anyone who has been told their attachment is "too big" without a number attached.
Resolution, in plain terms
DPI is how many pixels are rendered for each inch of the printed page. An A4 page is 8.27 inches wide, so:
| DPI | A4 page in pixels | Looks like |
|---|---|---|
| 72 | 595 × 842 | Fine at 100% zoom; small print softens when you lean in |
| 96 | 794 × 1123 | The old Windows screen standard — readable, unremarkable |
| 110 | 910 × 1287 | The usual sweet spot: crisp on a laptop and on a phone |
| 150 | 1240 × 1754 | Prints acceptably; footnotes and stamps stay sharp |
| 200 | 1654 × 2339 | Near print quality — only worth it with a generous byte budget |
Doubling DPI quadruples the pixel count, so it is the most expensive dial on the page. At a 300 KB target the automatic setting will usually land between 96 and 150 DPI depending on how many pages you have.
Colour or grayscale?
Grayscale is not just "remove colour". A JPEG stores brightness at full resolution and colour at half in each direction, so the two chroma planes together account for roughly a sixth to a third of a typical scan's bytes — more when the scan has coloured noise, which camera-based scans always do.
- Turn it on for black-ink documents, photocopies, printed letters, contracts and anything you will print in mono anyway.
- Leave it off for anything where colour carries meaning: a stamped certificate, a highlighted passage, a chart, an identity document, or a signature in blue ink where blue-versus-black is the point.
Why "300 KB" rarely comes out at exactly 300 KB
The search stops at the largest quality that still fits. Because JPEG output size moves in steps rather than continuously, the last accepted attempt is usually a little under the target — 291 KB, 297 KB, 283 KB. That is the correct behaviour: the alternative would be to overshoot and hand you a file the form rejects.
The result panel shows both numbers and a bar comparing them, plus the arithmetic the search used: your target, minus the estimated container overhead, divided by the page count. No step is hidden.
Compressing on a phone
This works on mobile, which matters because "get this under 300 KB" is very often a task someone is doing on a phone, standing in front of a deadline. Two practical notes:
- Mobile browsers cap how much memory a tab may allocate. A very large scan — say 40 pages at 600 DPI — can exhaust that and the tab will reload. Split the document first, or use a laptop.
- Rendering is CPU work, so expect roughly two to four times the wall-clock time of a laptop. Progress is per page, so you can see it moving.
Questions
Is 300 KB enough for a multi-page document?
For three to six pages of text-heavy scanning, yes — that is roughly 50 KB a page, which holds up at around 100 DPI. Photographic pages will look softer.
Why does my 300 KB result come out at 291 KB rather than exactly 300?
The search stops at the largest quality that still fits, and JPEG size moves in steps rather than continuously. Landing just under the target is the correct outcome; landing exactly on it would mean overshooting on the next attempt.
Can I keep colour?
Yes — colour is kept by default. There is a grayscale option under the advanced controls, which typically buys another 10 to 25 per cent if you need the headroom.
Does this work on a phone?
Yes. It is heavier than on a laptop, and a very large scan may hit the memory limit of a mobile browser, but a normal few-page document compresses fine on a phone.