Envelope Sizes Guide
Standard envelope dimensions for US and international mail.
| Envelope | Inches | mm | Fits |
|---|---|---|---|
| #10 (Business) | 4.125 x 9.5 | 105 x 241 | Letter folded in thirds |
| #9 | 3.875 x 8.875 | 98 x 225 | Letter folded in thirds |
| #6 3/4 | 3.625 x 6.5 | 92 x 165 | Personal letters |
| A2 (Invitation) | 4.375 x 5.75 | 111 x 146 | RSVP cards, invitations |
| A7 (Invitation) | 5.25 x 7.25 | 133 x 184 | 5x7 cards |
| 6x9 | 6 x 9 | 152 x 229 | Half-fold letter |
| 9x12 | 9 x 12 | 229 x 305 | Unfolded letter/A4 |
| C4 (ISO) | 9.02 x 12.76 | 229 x 324 | Unfolded A4 |
| C5 (ISO) | 6.38 x 9.02 | 162 x 229 | A4 folded once |
| C6 (ISO) | 4.49 x 6.38 | 114 x 162 | A4 folded twice |
| DL (ISO) | 4.33 x 8.66 | 110 x 220 | A4 folded in thirds |
Choosing the Right Envelope
For standard business correspondence in the US, the #10 envelope is the standard choice. For international mail, the DL envelope is most common. For unfolded documents, use 9x12 (US) or C4 (international). Invitation envelopes (A2, A7) are sized for greeting cards and invitations.