Which size to pick
Use the number you’ve been given if there is one: the form says “max 5 MB per file”, so type 5 MB.
For email, 10 MB parts are the safe choice. Gmail and Yahoo take about 25 MB per message and Outlook about 20 MB, but attachments are encoded on the way and grow by about a third. A 20 MB PDF can bounce from a 25 MB inbox. Two 10 MB parts won’t, and they leave room for the signature and any other attachment.
| Sending to | Each part under |
|---|---|
| Most email | 10 MB |
| A form that states a limit | that limit |
| A company mailbox that has bounced big files before | 5 MB |
How the parts are made
Pages stay whole and in order. We never cut a page in half or move pages around to pack them better, because a reader expects page 12 to follow page 11.
Each part is saved and then measured, not estimated. That matters more than it sounds. Pages in one PDF share fonts and images, so a part saved on its own needs its own copy of them. Adding up page sizes gets that wrong and can give you a part that’s over the limit. Every part here is checked against the real saved file.
Named so nothing goes missing
The parts are called report-part-1-of-3.pdf, report-part-2-of-3.pdf and so on. Whoever receives them knows the order and can see if one hasn’t arrived. Say in the email how many to expect too.
When a single page is too big
Some pages are bigger than the limit on their own, usually a high-resolution scan or a page with a large photo. That page becomes a part by itself, and the result tells you which page it was. The fix is to compress the PDF first, which shrinks the photos, and then split again. Often compressing alone is enough and you don’t need to split at all.
Before you split
If the file is already under the size you typed, you’ll be told, and there’s nothing to do. And if it’s a one-page PDF over the limit, splitting can’t help, but compressing can.
Splitting doesn’t lower the quality: every page is copied exactly. To put the parts back together later, Merge PDF sorts part-2 before part-10 for you.
Checked against the tool on 22 October 2026. How we write and test these guides