Envelope Sizes and Their Postage
Envelope size decides more of your postage than most people expect. A rectangle like the A7 mails for the plain$0.82 letter price at 1 oz. A square of almost the same area costs $1.31, because the sorting machines cannot orient it and a person has to handle it.
The table shows what each common size costs at 1 oz with nothing attached and the address written along the long side. Pick a size for the full breakdown, a pre-filled calculator and the closest cheaper alternative.
| Envelope | Size (in) | Fits a card up to | Mail class | 1 oz postage |
|---|---|---|---|---|
| A1 (4 Bar) | 3.625 x 5.125 | 3.5 x 4.875 | Standard letter | $0.82 |
| A2 | 4.375 x 5.75 | 4.25 x 5.5 | Standard letter | $0.82 |
| A6 | 4.75 x 6.5 | 4.5 x 6.25 | Standard letter | $0.82 |
| A7 | 5.25 x 7.25 | 5 x 7 | Standard letter | $0.82 |
| A7.5 | 5.5 x 7.5 | 5.25 x 7.25 | Standard letter | $0.82 |
| A9 | 5.75 x 8.75 | 5.5 x 8.5 | Standard letter | $0.82 |
| A10 | 6 x 9.5 | 5.75 x 9.25 | Standard letter | $0.82 |
| #10 | 4.125 x 9.5 | 3.875 x 9.25 | Standard letter | $0.82 |
| Tea length (4 x 9.25 card) | 4.125 x 9.5 | 4 x 9.25 | Standard letter | $0.82 |
| 5 x 5 square | 5 x 5 | 4.75 x 4.75 | Nonmachinable letter | $1.31 |
| 5.5 x 5.5 square | 5.5 x 5.5 | 5.25 x 5.25 | Nonmachinable letter | $1.31 |
| 6 x 6 square | 6 x 6 | 5.75 x 5.75 | Nonmachinable letter | $1.31 |
| 6.5 x 6.5 square | 6.5 x 6.5 | 6.25 x 6.25 | Large envelope (flat) | $1.69 |
How to read the table
Standard letter means the envelope runs through the machines and pays letter postage only.Nonmachinable letter adds a flat $0.49 to every piece. Large envelope applies once a side passes 6 1/8 in high or 11 1/2 in long, and starts at $1.69.
Sizes are the usual stationery trade sizes. Envelope makers vary by a sixteenth of an inch or so, which is why a size close to a limit deserves a ruler before you order 150 of them.