The #14 Business envelope has a width of 11 inches and a height of 5 inches, giving it a total surface area of 57.5 square inches. Its maximum enclosure size is 4.75 x 11.25 inches. This envelope is also referred to as the 14 envelope, corresponding to its height in inches.
The #14 envelope gets its numbering from William Irwin Martin's late 1800s system that standardized envelope sizes. As an increment above popular options like the #10 and #12, the #14 provides substantial vertical space for oversized contents. The #14's generous height capacity made it suitable for posters, calendars, magazines and other commercial mailings needing to stay flat and undamaged. While not as ubiquitous as smaller business envelopes, the #14 fills a key niche for enveloping tall documents and inserts with its expansive dimensions. It allows sizable contents to be mailed securely.