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 pounds 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 handbook that many states recognize as the authority on measurement law.
The US fluid gallon is about 14.1% smaller than the dry gallon, while its Imperial counterpart is about 3.2% larger.
Its implicit value in the US system was originally one eighth of the Winchester bushel, which was a cylindrical measure of 18.5 inches in diameter and 8 inches in depth, which made the dry gallon a non-terminating number of cubic inches and an irrational number whose value to four decimal places was 268.8025 (9.252 × π cubic inches ≈ 268.8025 in3). Since the bushel was later defined to be exactly 2150.42 cubic inches, this figure became the exact value for the dry gallon (268.8025 in3 gives exactly 4.40488377086 L).
- ""How Many? A Dictionary of Units of Measurement" by Russ Rowlett and the University of North Carolina at Chapel Hill". Archived from the original on 2012-02-18. Retrieved 2012-01-20.
- 101st Conference on Weights and Measures 2016. (2017). Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. National Institute of Standards and Technology. p. C-6, C-11, C-16.
- Summary of State Laws and Regulations in Weights and Measures Archived December 5, 2011, at the Wayback Machine. (2005) National Institute of Standards and Technology.