Dry gallon

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 8 lb of wheat. 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.

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 18.5 inch in diameter and 8 inch in depth, making it an irrational number of cubic inches; its value to seven significant digits was 268.8025 in3, from an exact value of 9.252 × π 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 ($268.803 cubic inches$ is $4.405 liter$).