Compress a PDF for email
Attachment limits are lower than they look, because email inflates every file it carries. Here is what the real ceilings are and how to get under them.
The compressor is on the front page. Set your target and go — nothing is uploaded.
Open the compressorThe limits that actually apply
| Service | Stated limit | Safe file size |
|---|---|---|
| Gmail | 25 MB | ~18 MB |
| Outlook.com | 20 MB | ~14 MB |
| Microsoft 365 / Exchange | 25 MB (often lowered to 10 MB) | ~7 MB |
| Yahoo Mail | 25 MB | ~18 MB |
| Corporate mail servers | Frequently 10 MB | ~7 MB |
Why the safe size is lower than the stated limit
Email cannot carry raw binary data, so attachments are encoded in base64 before sending. That encoding uses four characters for every three bytes, inflating the attachment by roughly a third. A 24 MB PDF arrives at the mail server as about 32 MB, which is why it bounces against a 25 MB limit that it appears to satisfy.
There is a second trap: the limit usually applies to the entire message, not each attachment. Three 8 MB files plus a signature image will exceed a 25 MB ceiling even though no single file comes close.
The practical rule is to target about 70% of the stated limit. For Gmail that means aiming for 18 MB, which is what the safe column above reflects.
How to compress for email
- Work out your recipient's limit, not just your own. Your message has to pass through their server too, and corporate servers are usually the strictest link in the chain.
- Open the compressor and load your PDF.
- Set the target in KB — 18 MB is 18000 KB.
- Compress, download, and attach the result.
Common questions
What is the Gmail attachment limit?
Gmail allows attachments up to 25 MB. Above that it offers to send a Google Drive link instead. The 25 MB ceiling counts the encoded size, so a file slightly under 25 MB on disk can still be refused.
What is the Outlook attachment limit?
Outlook.com allows 20 MB per message. Microsoft 365 and Exchange accounts default to 25 MB, but many company administrators lower it to 10 MB, which is why a file that sends fine from your personal account can bounce from your work one.
Why was my 24 MB attachment rejected?
Email encodes attachments in base64, which inflates them by roughly 33%. A 24 MB file becomes about 32 MB on the wire. Aim for around 18 MB of actual file to stay safely inside a 25 MB limit.
Should I just use a Drive or Dropbox link instead?
For anything above about 10 MB, usually yes. It avoids attachment limits entirely, lets you revoke access later, and does not clog the recipient's mailbox. Compression is the better answer when the recipient needs the file itself, such as a form submission or a legal filing.