Gmail's 25 MB sending limit counts the file before encoding, so a 20 MB PDF sends with room left for the message. On the way, base64 encoding adds about 37 percent, and a receiving server that counts that figure against 25 MB will refuse it. For that case, use the 18 MB Gmail target.
The tool works down in three stages and stops at the first that fits.
A file that is too big for email fails in one of three places: your provider refuses it, the encoded message exceeds a server limit, or the recipient's gateway bounces it. 20 MB passes Gmail and Outlook.com on the web, which count the file, and Microsoft 365's default, which counts the encoded message. It does not pass a 25 MB cap counted after encoding; the 18 MB target does. A default Exchange Server allows 10 MB after encoding, so the file needs to be about 7 MB. For anything larger than a few hundred pages of scans, a link is the right tool.
Where the 20 MB limit comes from
- Gmail25 MB, counted before encoding
- Outlook.com25 MB per file on the web, 20 MB in the Outlook app
- Microsoft 365, default35 MB after encoding, often changed by IT
- Exchange Server, default10 MB after encoding
- iCloud Mail20 MB before Mail Drop
Mail limits are not all counted the same way. Gmail and Outlook.com count the file; Microsoft 365 and Exchange count the encoded message, which is about 37 percent bigger. That gap is what catches most people out.
How the tool hits 20 MB
Add the PDF
Gmail's 25 MB sending limit counts the file before encoding, and 20 MB leaves room for the message around it. Encoding adds about 37 percent on the way, which matters where a server counts the encoded size.
Structure, then images against 20 MB
The free structural pass runs first. The images then come down from 200 ppi until the file is under 20 MB. The target is the file on disk and leaves no room for encoding.
Stage three, rarely needed for an attachment
Most documents clear a mail limit through the image ladder alone. A rebuild means a long scan, and the text layer keeps it searchable for whoever receives it.
Download, and read the result line
It shows the size of the file on disk, which is the figure Gmail checks. A server that counts the encoded message sees about 37 percent more.
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 20 MB, and what does not
More than an email will usually carry. The limit that catches people is not this one but the recipient's, which is applied separately and is often lower than their provider advertises.
When it cannot reach 20 MB
Attachments are refused for reasons that are not always about your file. Three moves, in order of how well they work:
- Send a link. Any shared link avoids attachment limits completely and delivers the file at full quality. For anything large this is simply the better answer.
- Find out what the recipient can receive. Their server decides, not yours. Corporate mail systems often stop well below 25 MB, and a message can leave your outbox and still be rejected.
- Split into two messages. Use Split PDF and number the parts in the subject line so they are easy to reassemble.
Why 25 MB is not always 25 MB
Mail was designed for text, so an attachment is converted to text-safe base64 before it leaves your outbox. That conversion makes it about 37 percent larger. Gmail checks its sending limit before the conversion, but a receiving server may check after it. A 20 MB PDF becomes about 27.4 MB in transit: Gmail sends it, and a server that applies 25 MB to the encoded message refuses it. The widget below does the arithmetic for your file against each provider.
When it still will not send
Two messages that arrive beat one that bounces
- Split PDF by range into halves
- Each part keeps full quality
- Recipients merge or file the parts as they wish
- Works with every provider and gateway
For anything over about 50 MB
- Drive, OneDrive and iCloud links carry any size
- The file stays under your control and can be revoked
- Some corporate recipients have link previews stripped
- Not an attachment: some workflows and archives need the file itself
Where people use the 20 MB target
- Signed contracts to a client's corporate inboxtext, fits
- Insurance claim packs with photographed evidencemixed
- Property packets to buyers, lawyers and brokersscans and photos
- Quarterly reports and diligence bundlesmixed
Why this runs in your browser
Attachments are usually contracts, invoices, statements or records. Uploading one to a compression site before emailing it means two parties receive it instead of one.
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 an attachment will not send.
01Why aim for 20 MB when Gmail allows 25 MB?
Gmail counts its 25 MB sending limit before encoding, and 20 MB sits under it with room for the rest of the message. Encoded, a 20 MB file is about 27.4 MB, so a receiving server that applies 25 MB to the encoded message would refuse it. For that case, use the 18 MB Gmail target.
02What if my file still will not fit?
Split it into parts and send two messages, use the 5 MB target if the recipient is on a default Exchange Server, which counts 10 MB after encoding, or share a link for anything over about 50 MB.
03Will the text still be readable?
Yes. Reaching about 20 MB rarely costs much, since the first rung of the ladder usually does it.
04Will the text still be selectable?
Yes, almost always. Attachments at this size do not normally need the pages rebuilt.
05What if the file cannot get under 20 MB?
You get the smallest attempt with its size. For anything large, a shared link is simply a better answer than an attachment.
06My file was already small. Why did it grow?
It returns an already-small file untouched. Encoding adds about 37 percent to that figure in transit, which matters where a server counts the encoded size.
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.