Compressing
How to Reduce a PDF to 100KB (Or Any Exact Size)
Upload forms that demand 100KB, 500KB or 2MB exactly. How to hit a hard target without ending up with a document nobody can read.
Government portals, university applications and job sites frequently insist on limits that were set when broadband was new. 100KB for a scanned certificate is a demanding target, and hitting it needs a strategy rather than a slider.
Work out whether it is achievable
Divide the target by the page count. 100KB over one page is tight but possible for a scan. 100KB over ten pages means 10KB a page, which for scanned images is not realistic at any readable quality.
If the maths says no, the answer is fewer pages, not more compression.
The sequence that works
- 1Remove every page the form does not require. This is by far the largest single saving.
- 2Convert colour scans to greyscale — roughly a third of the data disappears.
- 3Compress at a moderate setting and check the size.
- 4Step the compression up gradually, checking readability at each step.
- 5If you are still over, reduce the resolution rather than the JPEG quality — downsampling degrades text more gracefully than heavy re-encoding.
- 6Verify the document is still legible at 100% zoom before uploading.
Realistic targets
| Content | Achievable at readable quality |
|---|---|
| One page of text (not scanned) | Well under 100KB |
| One scanned page, greyscale | 80–150KB |
| One scanned page, colour | 150–400KB |
| One photograph | 100–300KB |
| Ten scanned pages | 800KB–2MB |
If it will not go small enough
Rescan rather than recompress. A document scanned at 150 DPI greyscale from the start is dramatically smaller than the same document scanned at 600 DPI colour and then crushed — and it looks considerably better, because you are not compressing detail you captured only to destroy.
Check before you submit
Open the finished file at 100% and read the smallest text on it — a reference number, a date of issue, a signature. Forms are rejected for illegibility as readily as for size, and a resubmission costs far more than the extra minute.
Do it now
Compress PDF
Reduce file size while maintaining quality. It runs in this browser tab — your file is not uploaded anywhere.
Open Compress PDFFrequently asked questions
Can any PDF be reduced to 100KB?+
No. A ten-page colour scan cannot reach 100KB and stay readable. Reduce the page count or rescan at a lower setting.
Why does the form insist on such a small file?+
Usually an old limit that nobody has revisited. It is rarely negotiable, so work within it.
Is it better to lower resolution or JPEG quality?+
Lower the resolution. Text degrades more gracefully when downsampled than when heavily re-encoded.
How do I check the exact file size?+
Your file manager shows it. Watch the units — some tools report MB where the form means MiB, which is a 5% difference at the boundary.