What is the Email Attachment Size Checker?
Prevents bounced email errors by warning senders about invisible Base64 attachment size inflation before sending.
How to Use This Tool
Enter your file size and select unit (MB or KB) to instantly verify compatibility across Gmail, Outlook, Yahoo Mail, ProtonMail, and iCloud Mail Drop.
Formula & Calculation Logic
The mathematical formula used to calculate this conversion is:
Encoded Size = File Size in Bytes × 1.3333 (Base64 encoding adds ~33% overhead)
Step-by-Step Example Calculation
Here is a real-world calculation example demonstrating the mathematics:
Example: A 20 MB PDF file attached to an email
After MIME Base64 encoding: 20 MB × 1.333 = ~26.67 MB
Result: FAILS Gmail limit (25 MB) and Outlook limit (20 MB)!
Frequently Asked Questions
Email systems transmit attachments as text using Base64 encoding, which expands binary files by approximately 33.3%. A 20 MB file becomes ~26.7 MB in transit, exceeding the 25 MB limit.
Upload the file to Google Drive, Dropbox, or OneDrive, or use file transfer services like WeTransfer, and share the link via email instead.