Mailing documents requires the perfect pairing between paper and envelope. Our Envelope Size Calculator helps you choose the correct ISO C-Series or North American envelope for your needs. Whether you're sending an unfolded A4 certificate in a C4 envelope or a tri-folded Letter in a #10 business envelope, our tool ensures your stationary is professional and correctly sized for the post.
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Standard Envelope Size Chart
Find the correct envelope size (C4, C5, C6, DL) for your paper dimensions. Fast, free, and 100% private. All processing happens locally.
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1
Enter Paper Size
Select the paper you want to mail (e.g., A4).
2
See Envelope
The tool recommends the appropriate envelope size.
3
Review Results
Verify the output looks correct before using or downloading it.
4
Save Your Output
Click the download or copy button to export your results to your device or clipboard.
Key Features
Paper-to-Envelope Mapping
Matches your document size (unfolded, half-folded, or tri-folded) to the correct envelope.
C-Series ISO Support
Complete dimensions for the international C4, C5, C6 and DL standards.
Business Envelope Guide
Includes North American standards like the #10, #9, and invitation (A-series) sizes.
Frequently Asked Questions
A C4 envelope fits an unfolded A4 sheet. A C5 fits an A4 folded in half.
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