Compress PDF to 100 KB, 500 KB or 1 MB – Reduce PDF to a Specific Size

Compress PDF to a specific size when a portal sets the limit

Upload forms are blunt. A scholarship portal says "PDF, maximum 200 KB", an application site says 500 KB, an email gateway stops at 1 MB, and the file is rejected if it is one byte over. A normal compressor makes you guess a quality setting, test the result, and repeat. This tool works the other way round: you type the limit, and it searches for the best quality that stays under it.

That is what makes it useful for anyone who has to compress a PDF to 100 KB, compress a PDF to 500 KB or compress a PDF to 1 MB for a deadline. It also handles the second annoyance of Indian and international portals, which is a required paper size. You can force every page onto A4, A3, A5, Letter or Legal in the same pass.

How to reduce a PDF to a specific size, step by step

1. 1
   Drop your PDF onto the box, or click it and choose the file. You can add several files and give them all the same limit.
2. 2
   In Target size, type the number from your portal. The box starts at 50.
3. 3
   Set Unit to KB or MB, matching the portal's wording.
4. 4
   Leave Page size on "Keep original" unless the portal demands a sheet size. Otherwise choose A4, A3, A5, Letter (US) or Legal (US).
5. 5
   Press Compress to Size and wait for the percentage to finish.
6. 6
   Read the result line, then press Download. If you added several files, use the ZIP button to take them all at once.

How the tool finds a file that fits

There are two routes, and the tool always tries the gentler one first. When Page size is left on "Keep original", it rewrites the document losslessly and measures the result. If that already fits under your limit, you get that file, the text stays selectable, and no quality is lost.

If the lossless file is still too big, or if you chose a forced page size, the tool renders every page with pdf.js and saves each as a JPEG inside a new document built with pdf-lib. It does this on a ladder of six attempts. The first renders at 1.5 times scale with JPEG quality 0.8, and each step after that lowers both: 1.2 and 0.68, then 1.0 and 0.58, then 0.85 and 0.48, then 0.7 and 0.38, and finally 0.55 and 0.3. After every attempt it checks the file size and stops at the first one that is under your limit.

That order is the whole point. You get the sharpest version that fits rather than the smallest version the tool can make, which are very different files.

Converting your limit into bytes

The tool treats 1 KB as 1,024 bytes and 1 MB as 1,048,576 bytes, which is how most operating systems report file sizes. A 200 KB limit is therefore 204,800 bytes, and 2 MB is 2,097,152 bytes.

Some portals count in thousands instead, so 200 KB means 200,000 bytes to them. The difference is 4,800 bytes, or 2.4 per cent. A file that lands at 202 KB by the tool's count would be rejected by such a site. If a portal has rejected a file that your computer shows as under the limit, type a slightly lower number, such as 190 for a 200 KB limit, and try again.

The number box takes whole numbers only. A decimal such as 1.5 is cut to 1, so for a one and a half megabyte limit type 1536 and choose KB. Leaving the box empty or entering 0 makes the tool fall back to 500.

A worked example: three scanned pages to 200 KB

Imagine a three-page scan of a marksheet and ID proof at 1,900 KB, and a portal that accepts 200 KB. Divide the limit by the page count and each page has about 67 KB to live in (200 divided by 3), before a few hundred bytes of document overhead.

A lossless rewrite of a scan does almost nothing, because the pages are already JPEG pictures, so the tool goes to the ladder. At the first rung each page is rendered at 892 by 1262 pixels, which is about 1.1 million pixels, and the document will probably still be above 200 KB. By the fourth rung the pages are 505 by 715 pixels, about 361,000 pixels each, a third of the first rung. If that attempt measures 187 KB, it is under 204,800 bytes and the tool stops and says the target was met.

The sizes in this example are illustrative, since real scans vary, but the pixel counts come straight from an A4 page of 595 by 842 points at those scales. If the pages had been mostly white with a few lines of print, the first rung might have been enough.

Setting an exact page size such as A4

Choosing a page size rebuilds every page on that sheet. A4 is 595.28 by 841.89 points, Letter is 612 by 792, and the others follow the standard measurements for A3, A5 and Legal. If your source page is landscape, the sheet is turned to landscape as well, so a wide scan is not squeezed onto a tall page.

The content is scaled to fit and centred, never cropped. Take an A4 page and force it onto Letter. The scale is the smaller of 612 divided by 595.28 and 792 divided by 841.89, which is 0.9407. The page becomes 560 points wide by 792 tall, centred on a 612-point sheet, leaving a white band of 26 points on each side. Nothing is cut off.

Because forcing a size means re-laying every page, it always uses the picture route. Text will not be selectable afterwards, even if your limit was generous. If you only want a smaller file and the portal does not check page size, leave the option on "Keep original".

Reading what the result line tells you

When the limit is met, the line shows the old size, the new size, and whether the pages were rasterised. For example, "1900 KB → 187 KB · target met. Pages were rasterised, so text is no longer selectable." When the lossless route was enough, it says the target was met without rasterising and that the text is still selectable.

When the limit cannot be met, you get the smallest result the browser could produce and a message that it could not reach your figure. That is useful information, not an error. It means the document needs another approach, such as fewer pages or a different file, and the next section covers those.

When the target is out of reach

A limit is unreachable when the pages simply hold too much information for the size. Twenty full-colour pages cannot become 50 KB without looking like smudges. Divide the limit by the page count first. As a rough guide rather than a fixed rule, a budget of only a few KB per scanned page is unlikely to be met.

There are three honest fixes. Take out pages you do not need, so fewer pages share the budget. Split the document into two uploads if the portal allows multiple files. Or start from a better source: a scan made at lower resolution in the first place, or a PDF exported from the original document, usually compresses far better than a photograph of a printout.

Common situations for a size-limited PDF

• Government and university application portals that give a different limit for each upload slot, such as 100 KB for an ID and 500 KB for a certificate.
• Job applications that accept a single PDF of 1 MB, which you can build by joining your documents and then compressing the combined file.
• Competitive exam and scholarship forms that insist on A4 pages.
• Visa and bank portals that publish limits in MB and reject without explanation.
• Email systems with a small attachment cap, where compressing before sending avoids a bounce.

Tips for a clean result

Compress last. Finish editing, signing and page ordering first, because every rasterising pass lowers quality and cannot be undone. If you need to add a signature, sign the PDF before you shrink it.

Scan in black and white or greyscale at a moderate resolution when the content is a printed page. A photograph of a document taken in poor light has noise that JPEG has to spend bytes on, and clean input compresses further at the same quality.

For a very small target, test with the pages you care about most. Zoom into the stamp, the signature and any small print on the downloaded file. If that detail is gone, ask whether the portal really needs it.

Mistakes to avoid

• Choosing a page size you do not need. It forces the picture route even when a lossless rewrite would have fitted.
• Typing KB when the portal said MB. A 2 MB limit entered as 2 KB cannot be met and wastes a run.
• Typing a decimal. 0.5 becomes 0, and 0 falls back to 500 in whichever unit is selected, so with MB chosen you would get a 500 MB limit and no compression. Enter 512 and choose KB instead.
• Running an already compressed file through again to squeeze out a few more KB. Quality only falls.
• Treating a rasterised file as editable. Keep the original if you may need the text later.

Limits, and where your file goes

Each PDF can be up to 100 MB and 500 pages, and encrypted or damaged files are refused with a pointer to unlocking or repairing them. The lowest rung of the ladder is 0.55 times scale at quality 0.3, which is equivalent to roughly 40 dots per inch, so there is a floor on how small a legible page can get.

All of the work happens inside your browser tab using your device's memory. Your documents are not uploaded to a Jobsixo server, which matters when the file is a certificate or an identity document.

Related tools

If you only need a general reduction and have no figure to hit, the level-based simple compressor is simpler. For photographs and signatures that must meet a KB range, use the exam form presets, which sets pixel size and file size together.