By extension of the American standards the half letter size meets the needs of many applications. It is also known as statement, stationery, Half A (from ANSI sizes) or simply half size. It is a piece of letter paper cut in half, 5.5 × 8.5 (140 × 216 mm).
https://en.wikipedia.org/wiki/Paper_size
Letter-Size Paper. Most printers sold for business use support standard 8.5 inch wide by 11 inch tall letter-size paper by default. At the same time, they can also feed the similar European specification A4 sheet, which measures approximately 8.25 inches wide by 11.75 inches tall.
http://smallbusiness.chron.com/standard-printer-paper-dimensions-58826.html
Comparison of Letter (shaded light blue) and Government letter sizes with some similar paper and photographic paper sizes. Letter or US Letter is a paper size for office use. It is the most common type in Canada, United States, and Mexico. It measures 8.5 by 11 inches (215.9 mm x 279.4 mm).
https://en.wikipedia.org/wiki/Letter_%28paper_size%29
The international paper size standard, ISO 216, is based on the German DIN 476 standard for paper sizes. ISO paper sizes are all based on a single aspect ratio of square root of 2, or approximately 1:1.4142. The base A0 size of paper is defined as having an area of 1 m 2.
https://en.wikipedia.org/wiki/Paper_size
Most business printers can accept a broad range of paper sizes within their sheet-fed paper trays. This flexibility lets you use one printer to handle everything from standard letter-and legal-size documents down to smaller pieces of paper like four-by-six photographic paper or even three-by-five cards. However, using differing sizes of paper can require you to reconfigure your printer.
http://smallbusiness.chron.com/standard-printer-paper-dimensions-58826.html
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.
https://en.wikipedia.org/wiki/Letter_%28paper_size%29
In 1996, the American National Standards Institute adopted ANSI/ASME Y14.1 which defined a regular series of paper sizes based upon the de facto standard 8 1⁄2 in × 11 in (215.9 mm × 279.4 mm) letter size which it assigned ANSI A. This series also includes ledger/tabloid as ANSI B.
https://en.wikipedia.org/wiki/Paper_size
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 (4.5 g), which is equivalent to 72 g/m2. The most common density of A4 paper is 80 g/m 2. The precise origins of the dimensions of US letter size paper (8.5 × 11 in) are not known.
https://en.wikipedia.org/wiki/Letter_%28paper_size%29
Outside of North America, Letter size may also be known as American Quarto and the size is indeed almost exactly one quarter of the old Imperial (British) paper size known as Demy 4to (17½×22½), allowing ½ for trimming.
https://en.wikipedia.org/wiki/Paper_size
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 (432 by 559 mm) paper at 70° F (21.11°C) and at 50% humidity.
https://en.wikipedia.org/wiki/Letter_%28paper_size%29
what are the dimensions of letter paper
The dimensions of a letter paper are 8.5 by 11 inches or 215.9 by 279.4 millimeters.