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Letter or US Letter is a paper size commonly used as home or office stationery in Canada, the United States of America, and Mexico. It measures 8.5 by 11 inches (215.9 mm x 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 in the rest of the world, 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, (), was used.〔(【引用サイトリンク】title= Why is the standard paper size in the U.S. 8 ½" x 11"? )〕 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 or 11 kg) – the weight of 500 sheets (a ream) of paper at 70° F (21.11°C) and at 50% humidity.〔Blocksma, Mary. Reading the Numbers. New York: Penguin Books, 1989.〕 One ream of 20-pound letter-sized paper weighs 5 pounds, 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. Thus these days when 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 wide and 10 to 11 inches 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. The related paper size known as half letter, statement, or organizer L is exactly one half of the US letter size (8.5 × 5.5 in). ==See also== * ANSI/ASME Y14.1 * ISO 216 (definition of metric paper sizes, e.g., A4) * Paper size: loose sizes 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Letter (paper size)」の詳細全文を読む スポンサード リンク
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