The U.S. gallon is defined in terms of volume, namely it is exactly 231 cubic inches. Multiplying that by (2.54 cm)^3 shows that it is thus 3785.411 784 cm3 (exactly). The first definition in the U.S., in 1832, was based on the Queen Anne wine gallon in use in Great Britain until 1824, one which had also been used in the colonies. The current definition is codified in the Mendenhall Order of 1893. You may wish to see my page at http://www.cofc.edu/~frysingj/background.htm for the dates 1832 and 1893.
Note that the gallon is used for liquid measurement and one-fourth of that is the liquid quart. The dry quart is defined as being one eigth of a half peck or one sixteenth of a peck, there being two pecks to a bushel. The bushel was originally intended to be the same as the Winchester bushel used in Great Britain until 1824, but ours missed it by a bit. The bushel here was defined by averaging the results obtained in a survey of measures in use in various customs houses in the colonies. See the above citation for more. Jim Terry Simpson wrote: > > >AFAIK, the US gallon is precisely defined as 5/6 imperial gallon, and > >the imperial gallon is exactly 10 pounds of water (presumably at 4C). > > I don't know if the US has a definition of an imperial gallon. > The following two countries have official definitions at: > > Ireland - Metrology Act 1996: > http://193.120.124.98/gen531996a.html > > UK - Units of Measurement Regulations 1995: > www.hmso.gov.uk/si/si1995/Uksi_19951804_en_2.htm -- James R. Frysinger Lifetime Certified Advanced Metrication Specialist Senior Member, IEEE http://www.cofc.edu/~frysingj [EMAIL PROTECTED] [EMAIL PROTECTED] Office: Physics Lab Manager, Lecturer Dept. of Physics and Astronomy University/College of Charleston 66 George Street Charleston, SC 29424 843.953.7644 (phone) 843.953.4824 (FAX) Home: 10 Captiva Row Charleston, SC 29407 843.225.0805
