You do not need to be a wizard at math, you can use this handy chart as a quick guide for your envelopes mail
Envelope Mailability:
To avoid a surcharge:
* The minimum size must be 3 1/2” x 5”.
* The maximum size must be 6 1/8” x 11 1/2”.
* The maximum thickness is 1/4”.
This template shows the minimum size mailing piece which will be accepted and the dimensions which are subject to surcharge for first- or third-class pieces weighing up to one ounce.
The aspect ratio of a mailing piece (the length divided by the height) should fall between 1.3 to 1 and 2.5 to 1. For example, a #10 envelope is 4 1/8 x 9 1/2. The aspect ratio is 2.3, so the envelope is mailable.
