Email attachment size calculator
Attachments get about a third bigger when they are sent, so a 20 MB file can be too big for a 25 MB limit. Enter your file sizes to see the real email size.
Why attachments get bigger
Email was designed for plain text. To send a file, your email app converts it to text with Base64 encoding, which turns every 3 bytes into 4 characters. That adds about 33%, plus a little more for line breaks. So:
| Your files | Size as an email |
|---|---|
| 5 MB | about 6.9 MB |
| 10 MB | about 13.7 MB |
| 15 MB | about 20.6 MB |
| 18 MB | about 24.7 MB |
| 20 MB | about 27.4 MB |
What to do when it's too big
- Send a link instead. Gmail offers Google Drive, Outlook offers OneDrive, and Apple Mail offers Mail Drop for large files.
- Zip the files, or resize photos before attaching them.
- Split them across several emails.
Remember that the receiver's server has a limit too. A message that leaves your account can still bounce with error 552 5.3.4.
Questions people ask
- What is the Gmail attachment size limit?
- Gmail lets you send up to 25 MB of attachments. Bigger files are sent as a Google Drive link.
- Why does a 20 MB file not fit in a 25 MB email?
- Encoding makes it about 27 MB, which is over the limit.
- Does zipping make files smaller?
- It helps a lot for documents and spreadsheets, but very little for photos, videos and PDFs, which are already compressed.