The #12 Business envelope has a width of 11 inches and a height of 4.75 inches, giving it a total surface area of 52.25 square inches. Its maximum enclosure size is 4.5 x 10.75 inches. This envelope is also referred to as the 12 envelope, corresponding to its height in inches.
The #12 envelope gets its numbering from William Irwin Martin's late 1800s system that standardized envelope sizes. Building on sizes like the #10 and #11, the #12 provides even more capacity with its ample height. The added vertical space made the #12 a popular choice for commercial mailings of posters, calendars, legal documents and other content requiring maximum height. While not as common as smaller options, the #12 fills a key niche as an envelope with expansive vertical space for long content needing to stay flat and undamaged. It allows businesses to send tall mail pieces securely.