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Email Attachment Size Calculator
Estimate whether an attachment fits a message budget after encoding.
YOUR NUMBERS, MADE CLEAR
⌗Calculate your result
How email attachment size calculator works
Base64 uses 4 × ceiling(bytes ÷ 3) bytes before line breaks. This calculator adds your estimated extra allowance. Headers, body text and other attachments need additional space.
A practical example
A 9 MB attachment needs approximately 12 MB for base64 alone.
Using this tool
- Replace the example values with your own measurements and units.
- Read the calculated result and any validation message.
- Copy the result for your notes; estimates depend on your inputs.
How should I interpret the result?
Base64 uses 4 × ceiling(bytes ÷ 3) bytes before line breaks. This calculator adds your estimated extra allowance. Headers, body text and other attachments need additional space.