PDF How to split a PDF by file size
To split a large PDF into smaller files by size, set a maximum file size and let the program cut the document into consecutive parts that each stay under it. In PDF BOOK Split you choose By file size, type the limit in MB, and press Split PDF. It runs offline on Windows 10 and 11, so the file is never uploaded.
Why splitting by page count does not solve a size limit
Pages in a PDF are not the same size. A page of plain text may weigh a few kilobytes, while a page with a scanned image or a full-page photo can weigh several megabytes. If you cut a book every 50 pages, one part may be tiny and another may still be too large for an email attachment or an upload form. A size limit has to be checked against the size of the real files.
How to split a PDF by file size
- Open the PDF in PDF BOOK Split, or drag the file onto the window.
- Choose By file size.
- In Largest file, type the limit in MB, for example 10. The smallest value accepted is 0.05 MB.
- Press Split PDF.
The program starts from the first page and puts as many whole pages as fit under the limit into the first file. It checks the size of what it actually wrote and adjusts, then continues with the next file until the last page is saved.
What you get
- Files are saved in a new folder next to your PDF. The original file is not changed.
- Names show the part number and the pages inside, like mybook_part_01_pages_1-37.pdf.
- Parts are consecutive and in order, so joining them again restores the book.
- Bookmarks that fall inside a part are copied into that part.
- Pages are never cut in half. If a single page is larger than your limit, it is saved as its own file, because it cannot be made smaller by splitting.
Splitting by size or by chapter?
| Your goal | Use |
|---|---|
| Fit an email attachment or an upload form | By file size |
| One file per chapter, named after the chapter | Book chapters (printed contents) or By bookmarks |
| Equal page counts, for example 10 pages each | Every N pages |
| Exact page ranges you already know | Page ranges, for example 5-12, 30-40, 55 |
All of these modes are in the same program. For the chapter methods, see how to split a PDF into chapters without bookmarks.
Limits
- The size limit is applied to the files the program writes. It cannot reduce the size of one very large page; for that you would need to compress or downsample the images first.
- Parts may come out somewhat under the limit, because only whole pages are used.
- Windows 10 and 11, 64-bit only. There is no Mac version.
Questions
How do I split a PDF into files under 10 MB?
Open the PDF in PDF BOOK Split, choose By file size, type 10 in the Largest file box and press Split PDF. Each saved file stays under 10 MB, built from whole consecutive pages.
Why is one of the parts larger than my limit?
A part can only be larger than the limit when it consists of a single page that is itself larger than the limit. A page cannot be divided, so it is saved alone.
Does splitting by size change the quality of my PDF?
The pages are copied into new files, not re-rendered or compressed, so text and images are kept as they are. Nothing is compressed, so the parts together can be slightly larger than the original, because shared items such as fonts are repeated in each part.
Are my files uploaded anywhere?
No. The splitting happens on your computer. There is no account and no upload.
Can I get one file per chapter instead?
Yes. Use the Book chapters mode with the printed table of contents, or By bookmarks if the PDF has bookmarks.
Windows 10 / 11 (64-bit) · Works offline · 30-day refund