Jonathan Scott said:
Well, the wiki says that the US gallon was originally the volume of a cylinder 6 inches deep and 7 inches in diameter, which comes to about 230.9 cubic inches and was subsequently rounded to 231 cubic inches by definition. However, that doesn't really "explain" very well where it came from.
Well, apparently the 231 cu. inches was adopted along time ago. It was an English thing, so one will have to track down the origin of the English wine gallon.As for US standards, the National Institute of Standards and Technology, formerly the National Bureau of Standards, in the Department of Commerce has some history. Weights and Measures were part of the Department of Treasury, and the US Constitution (Article I, Section 8) gives Congress the power to
“fix the standard of weights and measurement.”
From Measure for Progress, A History of the National Bureau of Standards, Department of Commerce, 1966.
http://www.nist.gov/nvl/upload/Measures_for_Progress-MP275-FULL.pdf
The gallon, based on the English wine gallon of 1703, was a vessel
with a volume of 231 cubic inches (holding 8.3389 pounds avoirdupois of distilled
water, or 58,372.2 standard grains) when weighed in air at 30 inches
barometric pressure and 62°F. The bushel, based on the old English Winchester
bushel, established in the reign of Henry VII, was a measure with a
volume of 2,150.42 inches (holding 77.6274 pounds avoirdupois of distilled
water or 543,391.89 grains), weighed at the same barometric pressure and
temperature as the gallon. (Hassler)
[Hassler,] "Weights and Measures", p. 12; Louis A. Fischer, "History of the standard
weights and measures of the United States," NBS M64 (1925), pp. 7-10. Note.-
M64 refers to the numbered series of Miscellaneous Papers of the NBS, as C designates
its series of Circulars.
The British abolished the wine gallon of 1703 and the Winchester bushel in 1824
when imperial measures were adopted. The imperial gallon was considered as 277.274
cubic inches of distilled water (10 pounds of water), the imperial bushel 2218.19
cubic inches (8 gallons of water), both at 62° F and 30 inches barometric pressure.
Thus as Peirce testified in 1885, the English and American gallons and bushels dif.
fered by about 17 percent and 3 percent, respectively, as they do today. Apothecaries'
weights in the two countries differ by almost 10 percent.Two years after the Treasury's adoption of Hassler's weights and
measures, the 1758 originals of the Troughton yard and Kater pound were
irreparably damaged by fire. Despite the fact that their prototypes were
lost, Congress recognized the merit and enormous convenience of the new
standards. if it could not bring itself to legalize them, it could at least
approve them, and in 1836—the generally accepted date of the establishment
of an Office of Weights and Measures in the Treasury—a joint resolution
of Congress directed the Secretary of the Treasury to make copies of
Hassler's standards, to be delivered to the governor of each State in the Union, or such
person as he may appoint, for the use of the States, respectively,
to the end that a uniform standard of weights and measures may
be established throughout the United States. (Quoted in NBS M64, pp. 10-12.)
Another history -
http://www.nist.gov/pml/wmd/pubs/upload/sp-447-2.pdf
God... 10 is such a jerk !.. 
... 
ps: This was only a joke, you know ... lol
D
I have a headache to imagine how long or large something is.
