Open side envelopes with square, often deep flaps and side seams, these envelopes - also called A-Style or A-Line -- can have deckle edges on the top flap and are often used with matching text and cover papers in white and colors.
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).
A-1
5.125 x 3.625
4.75 x 3.5
A-2
5.75 x 4.375
5.5 x 4.125
A-6
6.5 x 4.75
6.25 x 4.5
A-7
7.25 x 5.25
7 x 5
A-8
8.125 x 5.5
7.875 x 5.25
A-Long
(Slimline)
8.875 x 3.875
8.625 x 3.625
A-10
9.5 x 6
9.25 x 5.75
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.