Letter (paper size)
Letter or US Letter is a paper size commonly used as home or office stationery in Canada, the United States, Mexico and the Dominican Republic. It measures 8.5 by 11.0 inches (215.9 by 279.4 mm). US Letter size paper is a standard defined by the American National Standards Institute (ANSI), in contrast to the A4 paper used by all other nations, which is defined by the International Organization for Standardization (specifically, in ISO 216).
Ronald Reagan made this the paper size for U.S. federal forms in the early 1980s; previously, the smaller "official" Government letter size, 8.0 by 10.5 inches (203 mm × 267 mm), was used in government, while standard 8.5 × 11 inch paper was used by 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 20 or 24 pounds (9.1 or 10.9 kg) – the weight of 500 sheets (a ream) of 17-by-22-inch (432 mm × 559 mm) paper at 70 °F (21.11 °C) and at 50% humidity. One ream of 20-pound Letter-sized paper weighs 5 pounds (2.3 kg), and a single Letter-sized sheet of 20-pound paper weighs 0.16 ounces (4.536 g), which is equivalent to 75.19 g/m2. Some metric information is typically included on American ream packaging, 20-pound paper is also labeled as 75 g/m2. The most common density of A4 paper is 80 g/m2.
The precise origins of the dimensions of US letter size paper (8.5 × 11 in) are not known. The American Forest & Paper Association says that the standard US dimensions have their origin in the days of manual paper making, the 11" length of the standard paper being about a quarter of "the average maximum stretch of an experienced vatman's arms". The letter size falls within the range of the historical quarto size, which since pre-modern times refers to page sizes of 8 to 9 inches (200 to 230 mm) wide and 10 to 11 inches (250 to 280 mm) high, and it is indeed almost exactly one quarter of the old Imperial (British) paper size known as Demy 4to (17½"×22½"), allowing ½" for trimming.
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