The dry gallon, also known as the corn gallon or grain gallon, is a historic British dry measure of volume that was used to measure grain and other dry commodities and whose earliest recorded official definition, in 1303, was the volume of of wheat.[1] It is not used in the US customary system – though it implicitly exists since the US dry measures of bushel, peck, quart, and pint are still used – and is not included in the National Institute of Standards and Technology handbook that many US states recognize as the authority on measurement law.[2] [3]
The US fluid gallon is about 14.1% smaller than the US dry gallon, while the Imperial fluid gallon is about 3.2% larger than the US dry gallon.
The dry gallon's implicit value in the US system was originally one eighth of the Winchester bushel, which was a cylindrical measure of 18.5inch in diameter and 8inch in depth, making it an irrational number of cubic inches; its value to seven significant digits was 268.8025sigfig=7NaNsigfig=7, from an exact value of cubic inches. Since the bushel was later redefined to be exactly 2150.42 cubic inches, 268.8025 became the exact value for the dry gallon (is).