The following list shows the name/number designation, envelope dimensions, and approximate maximum enclosure dimensions for some of the more common sizes of this envelope style. Actual dimensions for enclosures will depend on the thickness of the enclosure (paper thickness, number of pages).
2
4.25 x 3.1875
4 x 2.9375
4
5.125 x 3.625
4.875 x 3.375
5
5.625 x 4.125
5.375 x 3.875
5 ¼
5.25 x 4.25
5 x 4
5 ½
5.625 x 4.375
5.375 x 4.125
6
6.5 x 4.75
6.25 x 4.625
Gladstone
5.5625 x 3.5625
5.375 x 3.375
Astor
5.625 x 3.625
5.375 x 3.5
Lee
7.25 x 5.25
7 x 5.125
All measurements in inches: .125 = 1/8 | .25 = 1/4 | .375 = 3/8 | .5 = 1/2 | .625 = 5/8 | .875 = 7/8
These envelope sizes apply specifically to the United States. Standard International envelope sizes differ.