Letter or US Letter is the most common paper size for office use in several countries, including the United States, Canada, Mexico, Bolivia, Colombia, Venezuela, the Philippines, and Chile. It measures 8.5 by 11 inches (215.9 mm × 279.4 mm).
Ronald Reagan made this the paper size for U.S. federal forms in the early 1980s; previously, the smaller "official" Government letter size, 8 in × 10.5 in (203.2 mm × 266.7 mm), was used.[1]
In the U.S., paper density is typically 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 17-by-22-inch (431.8 by 558.8 mm) paper at 70° F (21.11°C) and at 50% humidity.[2] 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 (4.54 g), which is equivalent to 72 g/m2 (72gsm)[3]
Unlike the A4 (210 × 297 mm) international standard (ISO) paper sizes which are used in most countries in the world today, the origin of the dimensions of letter size paper are lost in tradition. The American Forest and Paper Association argues that the dimension originates from the days of manual paper making, and that the 11-inch length of the page is about a quarter of "the average maximum stretch of an experienced vatman's arms".[1] However, this does not explain the width or aspect ratio.
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).