Envelope Size Converter
Find the right envelope dimensions and see which paper sizes fit inside (ISO 269 & US standards).
Standard Envelope Chart
C-Series Standard
The **C-series** (ISO 269) is designed specifically for A-series paper. A size **Cn** is the geometric mean of An and Bn paper, ensuring a perfect fit.
Folding Tip
If you don't want to fold your paper, match the number: **A4 fits in C4**. For one fold (half size), go up one number: **A4 fits in C5** when folded once.
Standard Envelope Size Chart
Find the correct envelope size (C4, C5, C6, DL) for your paper dimensions.
Enter Paper Size
Select the paper you want to mail (e.g., A4).
See Envelope
The tool recommends the appropriate envelope size.
Frequently Asked Questions
A C4 envelope fits an unfolded A4 sheet. A C5 fits an A4 folded in half.
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