Split a PDF into parts small enough to send

You have a PDF that a mail server or an upload form will not take. Set the largest size a part may be and the document comes back as several PDFs, each at or under it, in one zip. Every part is saved and weighed after each page is added rather than estimated, so the number on the form is the number on the file — and a megabyte here is 1,000,000 bytes, which is how mail servers and filing portals quote their limits.

It does not make anything smaller. Splitting a 40 MB scan gives you smaller files and the same total — compress the document first if the total is the problem.

Split by size

No account. Your upload is deleted after 2 hours, the result after 24 hours.

How it works

  1. Work out the real limit. Take the limit you were given and knock a third off. Gmail accepts a 25 MB message, which is about 18 MB of attachment once it has been encoded for sending; Outlook.com stops at 20 MB, so use 14. A portal that says 10 MB usually means the file itself, and 9 leaves a margin.
  2. Set the size and run it. Anything from 0.1 to 100 MB. The result says how many parts you got and how big the largest one is, so you can check it against the limit before you send anything.
  3. Send the parts in order. They are named after the original with -1, -2, -3 on the end, so whoever receives them can put the document back together. Say in the message how many there are.

What the options do

The form above lists the options this tool is running today, straight from the server. This is what they are for.

Largest file, in megabytes
The ceiling for each part, between 0.1 and 100. Each part is saved and measured for real after every page is added, because estimating is wrong in both directions on a PDF: pages sharing one embedded font or one scanned background cost almost nothing after the first, and objects are only compressed once they are written. That accuracy is also why the tool cannot tell you in advance how many parts you will get. A page bigger than the limit on its own cannot be halved, so it gets a file to itself and the result names it.

What this tool does not do

  • It does not make anything smaller. Splitting a 40 MB scan gives you smaller files and the same total — compress the document first if the total is the problem.
  • It cannot cut a page in two. A single oversized page comes back in a file of its own, over your limit, and the result tells you which page it was.
  • The parts add up to more than the original, because a font or an image used throughout has to be written into every part that needs it.
  • The parts are rebuilt documents: bookmarks are not carried over, and nothing marks where one part ends and the next begins except the numbering.
  • It does not know your mail server’s limit. The number on the form is the one it keeps to.

What happens to your file

The file is uploaded because Split PDF by size runs on our server rather than in the browser tab. It is kept for at most 2 hours and the result you download for 24 hours, then a scheduled job deletes both — a job has to be able to read the file while it runs, and you have to be able to retry a failed conversion without re-uploading. Neither needs longer.

Nothing about the contents is logged, and no one reads your documents. The retention page lists the same numbers the code enforces, and the privacy policy says who can reach the storage they sit in.

Questions

What size should I choose for Gmail?
About 18 MB. Gmail’s 25 MB limit applies to the whole message after encoding, and encoding an attachment adds roughly a third to its size. For Outlook.com, which stops at 20 MB, use 14.
Why is one of my files bigger than the limit I set?
Because a single page is bigger than the limit on its own, and half a page is not a thing. The result names the page. Run the document through compress first — an oversized page is nearly always a photograph scanned at a resolution nobody needed.
Why do the parts add up to more than the original?
Anything shared across the document — an embedded font, a logo, a background image — has to be written into every part that uses it. A ten-part split of a 30 MB file might total 33 MB, but each part is under your limit, which was the point.
Is a megabyte 1,000,000 or 1,048,576 bytes here?
It is 1,000,000, the same as your mail server means by it. Reading it the other way round would produce parts that are under the number you typed and over the limit you were given, which is the one outcome that would make the tool useless.
Can I split by size and keep the chapters together?
Not in one pass. Split by bookmarks first so each chapter is its own file, then run the oversized chapters through this. Two steps, but nothing lands in the wrong file.