Letter (paper size) "official" "Government Letter" size, , was used in government, while paper was standard in most other offices. In the U.S., paper density is usually measured in "pounds per ream" (of 500 sheets). Typical Letter paper has a basis weight of paper of – the weight of 500 sheets (a ream) of paper at and at 50% humidity. One ream of 20-pound Letter-sized paper weighs , and a single Letter-sized sheet of 20-pound paper weighs , which is equivalent to 75.19 g/m. Some metric information is typically included on American ream packaging. For example, 20-pound paper is also labeled as 75
Units of paper quantity sheets of vellum or parchment, i.e. 8 leaves, 16 sides. The term "quaternion" (or sometimes "quaternum") designates such a quire. A quire made of a single folded sheet (i.e. 2 leaves, 4 sides) is a "bifolium" (plural "bifolia"); a "binion" is a quire of two sheets (i.e. 4 leaves, 8 sides); and a "quinion" is five sheets (10 leaves, 20 sides). This last meaning is preserved in the modern Italian term for quire, "quinterno di carta". Formerly, when paper was packed at the paper mill, the top and bottom quires were made up of slightly damaged sheets ("outsides") to protect