Who asks you to compress PDF to 100KB?
Tiny limits show up where one website collects documents from a very large number of people. You may meet a 100 KB cap on:
- Government portals asking for an ID card, address proof or a birth certificate.
- Exam registration forms with a separate box for a signed declaration.
- Recruitment sites that take small supporting documents next to the application.
- Scholarship forms with five or six upload boxes, each with its own cap.
When a form says PDF in 100 KB or PDF 100 KB max, the file must be 100 KB or smaller, not exactly 100 KB. A 70 KB file passes, a 101 KB file is rejected. Read the instructions on the form itself, because some portals also set a minimum size or a page count.
How FileKiwi makes a PDF 100 KB or smaller
The tool does not guess one setting. It runs the same PDF through Ghostscript several times, each round with a lower image resolution, and keeps the first result that fits under your target:
| Round | Image resolution | What it means for a scan |
|---|---|---|
| 1 | 150 dpi | Close to the original, small print stays clear |
| 2 | 120 dpi | Still sharp on screen |
| 3 | 96 dpi | Good for reading on a phone or laptop |
| 4 | 72 dpi | Screen quality, fine print gets softer |
| 5 | 60 dpi | Normal text readable, stamps lose detail |
| 6 | 45 dpi | Only large print stays easy to read |
| 7 | 32 dpi | Last resort for very heavy scans |
Typed text and lines are not turned into pictures, so they stay sharp in every round. Only the images inside the PDF lose resolution, and on a scan that means the whole page. If your file is already 100 KB or smaller, you get it back unchanged.
What fits in 100 KB, and what does not
A form typed in Word and saved as PDF is often already under 100 KB. Scans are the challenge, because every page is a photo.
| Document | Chance of reaching 100 KB |
|---|---|
| One typed page | Very good, often small already |
| One page scanned in grayscale | Good after compression |
| A color phone photo of an ID card | Possible, it will look softer |
| A 6 page color scan | Unlikely, cut pages first |
Pages share the budget. Two scanned pages split the same 100 KB, so each loses more detail than a single page would.
100 KB PDF in bytes, KB and MB
Upload boxes count bytes, and not every website counts them the same way. This table shows what each wording usually means and what to type in the target size box:
| The form says | Limit in bytes | Type in the box |
|---|---|---|
| 100 KB | 102,400 (or 100,000 on some sites) | 95 |
| 0.1 MB | about 100,000 to 104,858 | 95 |
| Less than 100 KB | below 102,400 | 95 |
| 50 KB | 51,200 | 48 |
| 200 KB | 204,800 | use the 200 KB tool |
Check the size of your PDF file before you upload it:
- Windows: right click the file, choose Properties and read Size, not Size on disk.
- Mac: select the file in Finder and press Command and I. Finder counts 1 KB as 1,000 bytes, so a file of 102,400 bytes shows as 102 KB on a Mac and 100 KB on Windows.
- iPhone: in the Files app, touch and hold the PDF and choose Get Info.
- Android: in Files by Google, open the menu next to the PDF and choose File info.
Tips when the file will not get small enough
Send only the page that is required. Pull it out with Split PDF, then compress that single page.
Scan again in grayscale, with the paper flat and in daylight. Shadows and the desk around the edges cost bytes, so crop close to the paper.
If the upload box also takes JPG, Compress Image to 100 KB is often the easier route for a photo of one card. If the limit turns out to be larger, try Compress PDF to 200 KB to keep more detail.
A clean scan is the best start for a small file. Our guide on how to scan documents on iPhone covers flat pages, light and grayscale mode. If the portal also asks for a photo and a signature, reduce the photo size to 20 KB or 50 KB with the same care. For forms with a 200 KB limit and several documents, read how to compress a PDF for online forms.