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How to compress a PDF to 300 KB (and what to do if it won't fit)

Get a scanned PDF under 300 KB for a job, exam or government portal: the steps, what to try when it won't fit, and how to check the real file size.

Updated

Short answer: open Compress PDF to 300 KB, drop your PDF and press Compress PDF. The tool tries several resolution and quality settings and keeps the sharpest version that is still under 300 KB. If even the strongest setting can’t get there, the document has too many pages or too much colour for 300 KB: re-scan it in grey at a lower resolution, or split it into parts.

How to compress a PDF to 300 KB on Nibbo

  1. Open Compress PDF to 300 KB on your phone or computer.
  2. Drop the PDF onto the page, or tap it to choose a file.
  3. The Target size option is already selected, with 300 KB highlighted under Size limit. The current size of your file is shown next to it. If your portal asks for something else, pick another preset (100 KB to 5 MB) or choose Custom and type your own number.
  4. Leave Remove metadata, embedded page thumbnails and editor data ticked unless you need the document properties. It saves a little space and removes details such as the author name.
  5. Press Compress PDF. You’ll see Searching for the best fit… and each try with its size.
  6. When it finishes, the result line reads something like “292 KB, just under the 300 KB limit”. Press Download to save the file, which ends in -compressed.pdf.

Before you upload it, open the new file and zoom in on the small print: ID numbers, dates, stamps and signatures should still be readable. The compression happens in your browser, so the scan of your ID or certificate never leaves your device.

Why so many forms ask for 300 KB

Job portals, exam applications, scholarship forms and government services often cap each uploaded document at a few hundred kilobytes. They receive thousands of files for every application round, the people who check them only need to read the page on a screen, and small files upload reliably on slow mobile connections. 300 KB is a common cap for certificates, ID documents and mark sheets; 100 KB and 200 KB are common for photos and signatures.

The rules are set per portal and per document, and they change between application rounds. Read the instructions for your form: they usually give the size, the file type (PDF or JPG) and sometimes a resolution or page count.

Why your scan is so heavy

A PDF from a scanner or a phone is not text. Every page is a photo of paper.

Text and vector graphics, such as a CV exported from Word, are already tiny. That’s why compression helps scans enormously and documents typed on a computer hardly at all.

How the 300 KB budget works

300 KB is shared by all the pages, so the number of pages decides how much quality each one can keep. As a rough guide, 300 KB holds one or two scanned pages at about 100 to 150 DPI.

For reference, an A4 page is 1240 × 1754 pixels at 150 DPI, 827 × 1169 at 100 DPI and only 595 × 842 at 72 DPI. Below about 100 DPI, normal text is still legible on screen, but footnotes, stamps and handwriting blur quickly.

What Nibbo changes and what it keeps

Nibbo re-encodes the photos inside the PDF as JPEG at a lower resolution, measured against the largest size each image can appear on the page. In target mode it tries settings from gentle (220 DPI) to very strong (50 DPI) and searches between them, so the result lands as close under the limit as it can. Text, fonts and vector drawings are not touched, so a PDF that already has a text layer stays searchable. Tiny images and some special image types are left as they are.

When the PDF won’t go below 300 KB

If even the strongest setting is too big, Nibbo says Can’t reach 300 KB and shows the smallest size it could reach. You can still download that smaller file. Then try these, in this order:

  1. Remove pages you don’t need. Blank backs of pages, instruction sheets and duplicates all count. Organize PDF lets you delete pages before you compress.
  2. Re-scan in grey. For text documents, grey is the biggest single saving. On a scanner choose Grayscale and 150 DPI (200 at most). With your phone, use Scan document: it finds the corners of the sheet and crops away the background, and its Grey or Black & white look with Shadow removal gives clean white paper, which compresses much better than a grey, shadowy photo. Save as PDF, then run the result through the 300 KB compressor.
  3. Crop to the sheet. If you made the PDF from phone photos with JPG to PDF, the table and background around the page are wasted bytes. The scanner tool crops them for you.
  4. Split the document. If the portal allows several uploads (for example front and back of an ID, or one file per certificate), use Split PDF with By file size. Enter 0.3 MB for a 300 KB portal: like the compressor, that tool counts 1 MB as 1,000,000 bytes, so each part stays under 300,000 bytes. Pages are kept whole and in order.
  5. Ask for a different limit. If one page alone can’t reach 300 KB at a readable quality, a shrunk file may be rejected by the person checking it. Some portals allow a bigger size for certain documents; check the instructions.

If the result says the PDF has no photos or scans, the file is text and vector graphics. These are already compact, so the saving comes from removing pages or splitting, not from compression.

How to check the final size

Portals measure the file in bytes, and different systems turn bytes into “KB” in different ways. Nibbo aims for at most 300,000 bytes, which passes whether the portal counts 1 KB as 1000 or as 1024 bytes. Because of this, the same file can show as 293 KB on one device and 300 KB on another. Look at the byte count when it’s shown.

Nibbo’s own result also shows the new size before you download.

FAQ

Is 300 KB the same as 0.3 MB?

Yes, in decimal units: 300 KB = 0.3 MB = 300,000 bytes. Some systems use 1024 instead, where 300 KB is 307,200 bytes. A file under 300,000 bytes fits both.

Will compression make my document unreadable?

Usually not, for one or two pages. Text in the scan gets softer as the resolution drops, so check small print before you upload. If it’s blurry, use one of the fixes above instead of compressing harder.

The portal says my file is too big, but it shows 299 KB. Why?

Your device and the portal may count kilobytes differently, or the portal’s limit may be lower than you think. Check the exact byte count and keep the file under 300,000 bytes, or compress to 280 KB with Custom to leave some room.

Can I compress several PDFs at once?

The compressor takes one PDF at a time. If your documents belong in one upload, combine them first with Merge PDF and then compress the result; if they are separate uploads, compress each one.