The tool aims at 10 MB of file, with no room for encoding, which suits a portal that checks the file. In the mail, attachments gain about 37 percent when they are encoded, so for a default Exchange Server, which counts the encoded message against 10 MB, the file needs to be about 7 MB.
It works down in three stages and stops at the first that fits.
The 10 MB figure is the default message limit on Exchange Server and in the Outlook app for Exchange accounts. It also appears on client portals and some state court e-filing systems. Outlook.com allows 25 MB per file and iCloud Mail 20 MB per message, so neither needs this target.
Where the 10 MB limit comes from
- Exchange Server, default10 MB, counted after encoding
- Outlook app with an Exchange account10 MB by default
- Some state and county e-filing systems10 MB per document
- Client portals and secure message systems10 MB
- Government tender and procurement uploads10 MB
Exchange applies its 10 MB after encoding rather than before, which is why a file that looks compliant still bounces. A portal that checks the uploaded file adds no encoding overhead.
How the tool hits 10 MB
Add the PDF
The tool measures the file against 10 MB, the size a portal checks. Mail is different: attachments gain about 37 percent when they are encoded, so a default Exchange Server needs a file of about 7 MB.
Structure, then images against 10 MB
The structural pass costs nothing. The images then come down from 200 ppi until the file is under 10 MB. The target leaves no room for encoding, so it suits portals better than Exchange mail.
Stage three, seldom needed below this cap
Most documents reach this size without a rebuild. When one is required the pages are turned into pictures with the words kept searchable behind them, which for an emailed document is usually still acceptable.
Download, and read the result line
It shows the size of the file before encoding. Multiply by 1.37 for the size an Exchange server counts: a 10 MB file is about 13.7 MB there.
Structure, then the images in place, then the pages as pictures. It stops at the first stage that fits.
Untouched at the first two stages. If the pages do get rebuilt, an invisible text layer keeps them searchable.
The IDs, forms and statements people compress for portals never leave the device.
What fits in 10 MB, and what does not
A good deal, and more than most people expect. The encoding margin is the part that catches people out rather than the compression: this target is the file, and a mail server that counts the encoded message sees about 37 percent more.
When it cannot reach 10 MB
A file that clears 10 MB on disk can still be refused by a mail server. Three things to check:
- Remember the encoding overhead. Attachments gain about 37 percent in transit, so a 10 MB file arrives as about 13.7 MB. That is why a file that looks fine can still bounce; for Exchange, aim for about 7 MB.
- Send a link instead. For anything near the limit, a shared link avoids the problem completely and gives the recipient a file at full quality.
- Split into parts. Use Split PDF and send two messages. This is usually better received than a single message that fails silently.
Why 10 MB on disk is not 10 MB in the mail
Email cannot carry binary files directly. Every attachment is base64 encoded before it is sent, which inflates it by roughly 37 percent, and the gateway measures the encoded message. A 9 MB PDF on your disk is about 12.3 MB on the wire, over a 10 MB limit. The target on this page is the file size, so aim for the size that clears the cap after inflation: about 7 MB on disk for a strict 10 MB gateway.
Where people use the 10 MB target
- Signed agreements to a client on corporate mailtext, fits
- Inspection and audit reports with photosmixed, attempt 1 or 2
- State court filings with exhibitsmixed
- Design deliverables that must arrive as attachmentsimages
Why this runs in your browser
Anything being emailed is about to leave your control in any case, which is all the more reason not to give a copy to a compression service first.
The tool is right above
Everything on this page runs in your browser. Scroll up, drop the file, and keep it on your machine.
Common questions
What people ask when a file has to come under 10 MB.
01Why 10 MB specifically?
It is the default message limit on Exchange Server and a common cap on upload portals. Exchange counts the encoded message, so for Exchange mail the file needs to be about 7 MB; a portal that checks the file accepts the full 10 MB.
02My file is 9.5 MB and still bounced. Why?
Base64 encoding adds about 37 percent in transit, so a 9.5 MB file is about 13 MB on the wire. Aim for 7 MB on disk for a strict 10 MB gateway, or split the document into two messages.
03Will the text still be readable?
Yes. The first two stages recompress only the images and leave the text untouched.
04Will the text still be selectable?
Yes, almost always. Documents reach this size without the pages needing to be rebuilt.
05What if the file cannot get under 10 MB?
You get the smallest attempt, labelled honestly. For anything near a mail limit, sending a link avoids the problem entirely and keeps full quality.
06My file was already small. Why did it grow?
It returns an already-small file untouched. Remember that a server that counts the encoded message sees about 37 percent more.
07Are my files uploaded anywhere?
No. Rendering and compression run in your browser. The file never leaves the device.
08Is it free?
Free. Every tool, unlimited use, no signup.