Split a PDF by file size
cut locally · nothing uploaded
about this tool
This tool splits a PDF into the fewest consecutive parts that each stay under a size you set — 10 MB for a web form, 20 MB for Outlook, 25 MB for Gmail. Pages stay in order, nothing is recompressed, and each part is a complete PDF named with its page range.
Most splitters estimate sizes by dividing the file evenly, which fails because PDF parts don't add up: fonts and images shared by many pages are stored once in the original but once per part after splitting, so parts can come out larger than expected. This tool builds each candidate part and measures its real serialized size, searching for the largest run of pages that fits.
Email-safe mode fixes the other classic surprise. Mail servers measure attachments after base64 encoding, which inflates them by about 37%, so a 24 MB PDF bounces off a 25 MB limit. With the option on, the tool targets the encoded size and the parts actually arrive.
under the blade
- Algorithm
- Greedy, measured: each part is built and saved; exponential + binary search finds the boundary
- Guarantee
- Every part ≤ the limit, except a single page that is larger on its own (flagged)
- Email-safe
- Targets limit ÷ 1.368 (base64 4:3 + MIME line breaks) — 25 MB → 18.27 MB of PDF
- Quality
- Pages copied object-for-object; no image recompression
- Names
- name_part01_p1-34.pdf — part number and page range
- Units
- MB = 1,000,000 bytes, the conservative reading of provider limits
- Privacy
- Runs in your browser with pdf-lib; nothing uploaded
how it works
- 1 cm
Drop the large PDF
It opens locally; the gauge compares the file's size with your part limit.
- 2 cm
Set the limit
Type a size or pick a preset. Keep 'Sending by email' on if the parts are going out as attachments.
- 3 cm
Split, check, download
The tool measures and lists every part with its page range and exact size. Download them as a ZIP or one by one.
frequently asked questions
Why does my 24 MB PDF bounce from Gmail's 25 MB limit?
Because attachments are base64-encoded for transport, which makes them about 37% larger. Gmail's 25 MB limit applies to the encoded message, so the largest PDF you can attach is roughly 18 MB. Email-safe mode accounts for this automatically.
Why are the parts bigger than file size ÷ number of parts?
Shared resources. A font or logo used on every page is stored once in the original, but each part needs its own copy. That's why this tool measures every part's real size instead of dividing evenly.
What if a single page is bigger than the limit?
It's placed in its own part and flagged — a split can't go below one page. Those pages are usually high-resolution scans; reduce their image resolution or raise the limit.
Does splitting by size compress or change my pages?
No. Pages are copied as-is with pdf-lib, so text, fonts and image quality are untouched. If the parts are still too large overall, compression is a separate step.
Is my document uploaded?
No. The PDF is opened, measured and split entirely in your browser tab — useful for contracts, medical records and statements that shouldn't pass through someone else's server.