User:Milton Beychok/Sandbox

At one time, the volume of a gallon depended on what was being measured, and where it was being measured. But, by the end of the 18th century, three definitions were in common use:

• The corn gallon, or Winchester gallon, of about 268.8 cu in (≈ 4.405 L),
• The wine gallon, or Queen Anne's gallon, which was 231 cu in (≈ 3.79 L), and
• The ale gallon of 282 cu in (≈ 4.62 L).

The corn or dry gallon was used in the United States until recently for grain and other dry commodities. It is one eighth of the (Winchester) bushel, originally a cylindrical measure of Template:Frac inches in diameter and 8 inches in depth. That made the dry gallon (Template:Frac)² × π cu in ≈ Template:Val. The bushel, which like dry quart and pint still sees some use, was later defined to be 2150.42 cubic inches exactly, making its gallon exactly Template:Val (Template:Val). In previous centuries, there had been a corn gallon of around 271 to 272 cubic inches.

The wine, fluid, or liquid gallon has been the standard U.S. gallon since the early 19th century. The wine gallon, which some sources relate to the volume occupied by eight medieval merchant pounds of wine, was at one time defined as the volume of a cylinder six inches deep and seven inches in diameter, i.e. 6 × (Template:Frac)² × π ≈ Template:Val. It had been redefined during the reign of Queen Anne, in 1706, as 231 cu in exactly (3 × 7 × 11 in), which is the result of the earlier definition with π approximated to Template:Frac. Although the wine gallon had been used for centuries for import duty purposes there was no legal standard of it in the Exchequer and a smaller gallon (224 cu in) was actually in use, so this statute became necessary. It remains the U.S. definition today.

The original ratio between corn and wine gallons was (Template:Frac)²:6 × (Template:Frac)² = 1369:1176, but 268.8:231 (i.e. the ratio between the rounded quantities, in cubic inches) is exactly 64:55 or approximately 13:11. This approximation is still applicable, although the ratio of Template:Val slightly changed to Template:Val with current definitions (268.8025:231 = Template:Gaps:Template:Gaps ≈ 1351:1161). In some contexts, it was necessary to disambiguate between those two U.S. gallons, so "liquid" or "fluid" and "dry" respectively were added to the names.Template:Citation needed

In 1824, Britain adopted a close approximation to the ale gallon known as the Imperial gallon and abolished all other gallons in favour of it. Inspired by the kilogram-litre relationship, the Imperial gallon was based on the volume of 10 pounds of distilled water weighed in air with brass weights with the barometer standing at 30 inches of mercury and at a temperature of 62 °F. In 1963, this definition was refined as the space occupied by 10 pounds of distilled water of density Template:Val weighed in air of density Template:Val against weights of density 8.136 g/mL. This works out at approximately Template:Val (Template:Val). The metric definition of exactly Template:Val cubic decimetres (also Template:Val after the litre was redefined in 1964, ≈ Template:Val) was adopted shortly afterwards in Canada; for several years, the conventional value of Template:Val was used in the United Kingdom, until the Canadian convention was adopted in 1985.

Before and into the 19th century there were also several other gallons in use, with varying definitions. These are summarized in the table below. During some eras, the gallon was based on an exact conversion with a linear measure cubed. Other eras, the gallon was based on a rational approximation to the volume of a cylinder that could be used as a standard container, such as a basket, barrel, or jar. Other definitions were based on the density of a commodity, occasionally water, but more often a more marketable good such as wine or oats. Given these options and the variety of cultures that have used the gallon, it is not surprising that the exact value has drifted over the centuries.