The 9 1/2 Booklet envelope has a width of 12 inches and a height of 9 inches, giving it a total surface area of 108 square inches. Its maximum enclosure size is 8.75 x 11.75 inches. This booklet envelope is sometimes referred to as the 9-1/2 catalog envelope.
Booklet envelopes like the 9 1/2 get their sizing from the height and width in inches rather than a numbering system. The 9 1/2 booklet has an open side seam for easy insertion of flat contents without folding. The "1/2" indicates this envelope is slightly wider and taller than the 9 booklet. The incremental size increase provides additional room for larger products like catalogs, magazines, documents and items requiring flat, protected mailing. With dimensions between the 9 and 10 booklet envelopes, the 9 1/2 serves a niche for mailings needing more space than a 9 but less than a 10 booklet.