The #7 Business envelope has a width of 6.75 inches and a height of 3.75 inches, giving it a total surface area of 25.31 square inches. Its maximum enclosure size is 3.5 x 6.5 inches. This envelope is also referred to simply as the 7 envelope, corresponding to its height in inches.
The #7 envelope gets its numbering from William Irwin Martin's late 1800s envelope standardization system. The increment from #6 to #7 indicates a slightly taller envelope better suited for holding additional content. With its extra height compared to the #6 envelopes, the #7 became popular for business mailings needing more vertical space. It works well for invoices, statements, brochures, and other commercial content requiring just a bit more room. The #7 offers efficiency and versatility for transactional and advertising mailings. Today it remains one of the most ubiquitous business envelope sizes.