United States gallon

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In the United States, the only legal gallon is a unit of liquid capacity = 231 cubic inches = 3,785.411 784 cubic centimeters. This is not the only gallon that has been used in the United States; for example, in the late 19th century some states had a 282-cubic-inch “milk gallon.” And see U.S. dry gallon. Symbol, gal.

The state of New York had a liquid gallon defined in law as the volume occupied by 8 pounds avoirdupois of water at 39.83 degrees Fahrenheit at a barometric pressure at 30 inches. That would make it about 221.184 cubic inches. It was abolished by an act of 11 April 1852.

The United States gallon descends from the English wine gallon.

Sources

The gallon is a vessel containing 58372.2 grains (8.3389 pounds avoirdupois) of the standard pound of distilled water, at the temperature of maximum density of water, the vessel being weighed in air in which the barometer is 30 inches at 62° Fahrenheit. ... These standards were adopted by the Treasury Department on the recommendation of Mr. Hassler, in 1832.

U. S. Senate, 34th Congress, 3rd Session.
Ex. Doc. No. 27.
Report of the Secretary of the Treasury on the Construction and Distribution of Weights and Measures.
Washington: A. O. P. Nicholson, printer, 1857.
Page 5.