How to compress a PDF to under 1 MB, 500 KB or 100 KB

The quickest way: To a size

The tool above opens on To a size with a limit of 1 MB. For another limit, tap 100 KB, 200 KB or 500 KB, or type your own number in Target size.

1. Add the PDF, or a whole folder of them.
2. Check the limit, then press Compress.
3. Each file shows its size before and after, and the settings it was fitted at.
4. Download. Several files come back as a single ZIP.
5. Open the result and zoom in. Make sure the smallest print, signatures and stamps are still readable before you send it.

Behind that button, the tool tries the options that cost your document least, in order. A file already under the limit is left exactly as it was. A file that fits after a lossless rebuild keeps its selectable text. Only if neither works are the pages redrawn, starting at 150 dpi and high quality and stepping down only as far as the limit forces.

Here is what it did in our own test, with synthetic 300 dpi scans of printed A4 pages, run in a browser with the same tool:

Your documents will differ, because size depends on what is on the page. A white page of text shrinks far more easily than a page of photographs or a coloured background. The pattern holds, though: the more pages and the tighter the limit, the lower the settings have to go.

The kilobyte trap

One thing gets files rejected with no explanation. Some sites count a kilobyte as 1,000 bytes and others as 1,024, so a file sized to the looser count can be refused by a stricter site.

To a size always uses the stricter count, 1 KB = 1,000 bytes, so a file made for 500 KB fits either way. The sizes shown in the results list use 1,024, which is why a 500,000 byte file shows as about 488 KB there. Both are correct; they are just counting differently.

Setting it yourself

Choose Shrink hard if you would rather pick the resolution and quality yourself. These are sensible starting points:

On a manual setting, check the size yourself and aim about five percent under the limit, to allow for the kilobyte difference above.

Keeping small print readable

Resolution decides how much detail survives. At 96 dpi an A4 page is redrawn at about 794 × 1,123 pixels; at 72 dpi, about 595 × 842. Ordinary text reads fine at both, but very small print, such as a certificate number or a faint stamp, can start to blur at 72 dpi.

Quality decides how coarsely the image is stored. Pushed too low, JPEG blocks and smudges appear around letters. That is why To a size will not go below quality 48 while it can still lower the resolution instead. In our two page test, that rule is what made it choose 120 dpi at quality 72 rather than 150 dpi at quality 30 for a similar file size.

When a PDF will not get small enough

• Send only the pages that were asked for. A long document will not fit a tight limit and stay readable. Take the pages you need with the PDF splitter, then compress them.
• Drop blank pages and covers, which scanners love to include.
• Start from photos, not from a PDF. If you photographed the document yourself, build the PDF with JPG to PDF on Smallest file. In our test, two photographed A4 scans became a 108 KB PDF that way.
• Merge after compressing, not before. If a form wants several documents in one PDF, compress each, then combine them with PDF merge and check the total.

Keeping the document private

The PDFs people need to shrink are usually the personal ones: IDs, payslips, certificates, contracts, medical letters. Many compression sites upload them first. The tool above never receives your file at all. It is compressed inside your browser, which you can confirm for yourself.