The 9 Booklet envelope has a width of 11.5 inches and a height of 8.75 inches, giving it a total surface area of 100.63 square inches. Its maximum enclosure size is 8.5 x 11.25 inches. This booklet envelope is sometimes referred to as the 9 catalog envelope.
Booklet envelopes like the 9 get their sizing from the height in inches rather than a numbering system. The 9 booklet has an open side seam allowing easy insertion of flat documents without folding. Its ample width and height provide room for larger products like catalogs, magazines, posters and documents requiring flat, protected mailing. The open side prevents creasing and damage. With dimensions substantially larger than smaller booklet options, the 9 booklet serves needs for enveloping big, flat pieces. Its size efficiency makes it popular.