How to split a large PDF to get under an email size limit

By Nasir Uddin Shamim · Founder, PrintxPDF

Updated 2026-08-24 · 7 min read

Short answer: Gmail allows 25 MB per message and Outlook.com allows 20 MB, but Base64 encoding inflates attachments by about a third, so aim for 18 MB or less. Compress the PDF first; if it is still too big, split it into numbered parts that each land under that ceiling.

Two numbers decide this: what your provider allows, and what the recipient's provider allows. The smaller of the two wins, and you do not know the second one. That is why the practical target is lower than any published limit.

The limits, and the hidden third

Service	Sending limit	Receiving limit	What happens above it
Gmail	25 MB per message	Up to 50 MB	Auto-uploads to Google Drive and inserts a link
Outlook.com	20 MB	20 MB	Prompts you to use a OneDrive link instead
Microsoft 365 / Exchange Online	25 MB by default	25 MB by default	Admins can raise it to 150 MB; most do not
Yahoo Mail	25 MB	25 MB	Rejected
iCloud Mail	20 MB	20 MB	Mail Drop takes over, up to 5 GB, links expire after 30 days
Proton Mail	25 MB total per message	25 MB	Rejected
Most corporate servers	10-25 MB	10-25 MB	Silently bounced, sometimes with no notice to you

Attachment limits as of 2026. Sending limits are the ones that bite.

The hidden third is encoding overhead. Email attachments are Base64-encoded for transport, which represents every 3 bytes as 4 characters. That is a 33 percent increase, plus line breaks. A 20 MB PDF becomes about 27 MB on the wire, and a 25 MB stated limit usually applies to the encoded message, not to your file.

Note: Aim for 18 MB per attachment. That leaves room for Base64 expansion under a 25 MB ceiling, plus headers and the message body. Under a 20 MB ceiling, aim for 14 MB.

Compress first. Almost always.

Splitting is a workaround; compression is a fix. The recipient gets one attachment instead of four, nobody has to reassemble anything, and the document stays whole. Try it first and only split if compression is not enough.

How much you can expect to save depends entirely on what is making the file big:

What is in the PDF	Typical size before	After compression	Why
300 DPI colour scans	1-3 MB per page	100-300 KB per page	Downsampling to 150 DPI plus better image encoding
Phone photos placed on pages	3-5 MB per page	200-500 KB per page	12 megapixels is far more than a page can show
Text and vector graphics only	Under 200 KB per page	Barely changes	There is nothing to downsample
Presentation slides exported to PDF	500 KB-2 MB per slide	150-400 KB per slide	Background images and embedded fonts
Signed or certified documents	Any	Do not compress	It would invalidate the signature

Try compression before splitting. A 60 MB scan usually lands between 5 and 10 MB.

Deciding what to do

Situation	Do this
40 MB of scans, mostly images	Compress. It will almost certainly fit in one message.
22 MB, already compressed, text-heavy	Split into two parts of about 11 MB each.
200 MB video-embedded or archival file	Do not email it. Share a cloud link.
Legal or signed document that must not change	Split, never compress. Compression re-encodes and breaks signatures.
Recipient is on a corporate server with a 10 MB cap	Split into 7 MB parts, or use a link.
You do not know the recipient's limit	Keep each part under 10 MB. It is below every common ceiling.
Recipient asked for one file	Compress hard, or share a link, and say why.

Pick the route that matches the file and the recipient.

Splitting it properly

Work out the chunk size Divide the file size by your per-message target. A 68 MB PDF with an 18 MB target needs 4 parts, so round up and aim for 4 or 5.
Convert that to pages Divide the page count by the number of parts. A 68 MB, 240-page file split into 5 gives 48 pages per part. Use the every-N-pages mode with N = 48.
Split at a sensible boundary Nudge the boundaries so parts break between chapters or sections rather than mid-sentence. Custom ranges are worth the extra typing here. See splitting into pages or ranges.
Check every part Sizes are rarely even, because pages are not equally heavy. One 90-page part of thin text can be smaller than a 20-page part of scans. Verify each file individually against your target.
Name them for the recipient Use Report_2026_part1of4.pdf rather than Report (1).pdf. The person on the other end has to work out the order without you.
Send in order, one per message Say in the first message how many parts there are, and mention how to reassemble them if the recipient needs the whole document.

Split by page count or by custom ranges, with the page count for each part shown before you commit.

Watch out: Never split a PDF into parts and then compress each part separately if the document is being submitted somewhere official. Page numbering, signatures and any certification will not survive, and a reviewer receiving four unrelated-looking files is a good way to have a submission rejected.

The option most people should take instead

Splitting a document across four emails is a bad experience for whoever receives it. A link is better in almost every case where it is allowed:

Google Drive, Gmail does this automatically above 25 MB, uploading the file and inserting a link. Check the sharing permission it applies, because the default may be narrower than the recipient needs.
OneDrive, Outlook offers the same thing, and Microsoft 365 accounts include 1 TB.
iCloud Mail Drop, up to 5 GB, built into Apple Mail, links expire after 30 days.
WeTransfer and similar, up to 2 GB on the free tier, no account required for the recipient.
For anything confidential, check whether your organisation permits these services before using one. Many do not.

Why the PDF is large in the first place

Worth knowing, because it changes what you should do. A 50 MB PDF is almost always one of three things: a scanned document stored at 300 or 600 DPI, a set of pages carrying full-resolution photographs, or an export from design software that embedded every asset at print resolution. All three compress dramatically. A 50 MB PDF that is genuinely mostly text is rare, and usually means the file has accumulated revision history through incremental saves, which a full rewrite clears out.

If the file came from a scanner, also run OCR while you are at it. It adds a small amount of size and makes the document searchable, which is what the recipient will want next anyway.

Frequently asked questions

What is the maximum attachment size for Gmail?

Gmail allows 25 MB for a message you send and can receive up to 50 MB. Above 25 MB it uploads the file to Google Drive and inserts a link instead. Because attachments are Base64-encoded, aim for about 18 MB of actual file to stay under the ceiling.

What is the Outlook attachment size limit?

Outlook.com caps attachments at 20 MB. Microsoft 365 and Exchange Online default to 25 MB, which an administrator can raise to 150 MB, though most organisations leave the default in place.

Should I compress or split a large PDF?

Compress first. It keeps the document as one file, and a scan-heavy PDF typically drops by 80 to 90 percent. Split only when compression is not enough, or when the document is signed or certified and must not be re-encoded.

How do I split a PDF into equal parts by file size?

Divide the total size by your per-message target to get the number of parts, then divide the page count by that number and split every N pages. Check each part afterwards, because pages vary in weight and the split will not be perfectly even.

Why does my 24 MB PDF bounce from a 25 MB limit?

Attachments are Base64-encoded for transport, adding roughly 33 percent, so a 24 MB file travels as about 32 MB. The limit applies to the encoded message including headers, which is why the practical maximum is around 18 MB.