Compress PDF to 100KB — Free, Fast & Private
A 100 KB limit is the tightest one most people meet on an upload form, and it is tight in a way that surprises people: it is about the size of one modest phone photo, and the form wants a whole document in it. This page opens the MiniPx PDF compressor with its target already at 100 KB, so the job is to drop the file, press Compress and read the number. What follows is how the tool gets there, what it costs you, and the one decision that usually matters more than any compression setting — how many pages you are sending.
How the 100 KB target is met
Every page of your PDF is rendered in the browser and re-encoded as a JPEG image (each page keeps its original page size), then the document is rebuilt around those images. With a target set, the JPEG quality is not a fixed level: a byte search picks it page by page, and if quality alone cannot get under the budget the page image is also reduced in pixel dimensions, in steps, while the page itself keeps its exact size. The finished document is then measured. If it lands at or under 100,000 bytes you see that measured size; if it does not, the tool says the target was not reached and shows the smallest size it managed.
The kilobyte here is decimal, so 100 KB means 100,000 bytes. A file that fits under 100,000 bytes also fits a portal that counts a kilobyte as 1,024 bytes, so the decimal reading is the safe one for either kind of form. One consequence you will notice: the size readout in the tool divides by 1,024, so a result that meets the target shows a number a little under 100 KB — 99,594 bytes reads as about 97.3 KB (99,594 ÷ 1,024). That is the same file, counted the other way.
The page keeps its exact paper size through all of this. An A4 scan comes back as A4, so a form that checks the page format as well as the byte count sees the same page it would have seen before; what changes is the resolution of the picture on it.
At 100 KB, page count decides more than compression
The budget is shared across the whole document, which makes the arithmetic blunt. Each page gets roughly its share:
| Pages in the PDF | Roughly per page |
|---|---|
| 1 | 100 KB |
| 2 | 50 KB |
| 4 | 25 KB |
| 10 | 10 KB |
The document structure takes a little of that too, so the real per-page figure is slightly lower than the table. A single scanned certificate has the whole 100 KB to itself. Ten pages at about 10 KB each leave far less room for small print. So before you compress, check whether the form actually wants every page. Many forms ask for one document per box — a mark sheet in one, a certificate in another — and splitting a combined scan into the pieces the form asks for buys more legibility than any setting can. Removing a blank back side or a cover sheet does the same.
One measured run, not a promise
We put a real four-page scanned PDF of 8,538,448 bytes (8.1 MB as the tool shows it) through this page on the built site. On the 100 KB target it came out at 99,594 bytes, in 7 to 9 seconds in Chromium on a laptop. That is about 25 KB a page. Look at your own result before you submit it; the measured size tells you it fits, not that it is legible. It is one file on one machine. A scan with dense photographs, more pages or a slower phone will take longer and may not fit, which is why the tool measures and reports every result instead of assuming.
When 100 KB cannot be reached, you get a red notice: the target was not reached, this is the smallest the PDF could be made, and an upload form enforcing 100 KB will refuse it. If that smallest version is still smaller than your original you can download it, for example to try a looser limit elsewhere. If the result is not smaller than what you started with, nothing is offered and you keep your original.
What you give up, and where it stays private
This method turns every page into a picture. Selectable text does not survive — it becomes part of the page image, so it can no longer be searched or copied. For a scan that was already a picture of paper, nothing is lost. For a PDF exported from a word processor, it is the wrong tool; the tool checks the first pages when you choose the file and warns you if it finds live text. Colour on a size target comes back as standard sRGB, which on an ordinary scan makes no visible difference. The rendering, compression and rebuilding all run in this browser tab, and the PDF is never uploaded, which matters for the identity papers and certificates that usually meet a limit this small. Portals differ, so read the limit your own form states, and if it asks for something other than 100 KB, the 200 KB, 500 KB and 1 MB options are one click away above.
The KB-first version of this task is reduce PDF size in KB; a photo-based PDF is built on JPG to PDF under 100KB.