Definition of Gallon

The gallon is a measurement unit for volume and the capacity of fluid in both US customary units and the British Imperial systems of measurements. There are four quarts and eight pints in a gallon and they too have different measuring values and capacity in different measuring systems.
Worldwide usage of gallons

The gallons are used in fuel economy expression in United Kingdom and Canada are the Imperial gallon system. Despite its status as a US territory and unlike American Samoa, the Northern Mariana Island, the US Virgin Islands, Guam, Puerto Rico ceased selling gasoline by the US gallon system in 1980.

The US gallon is also used in several other countries along with United States of America. The countries where US gallon is used for the purpose of selling gasoline are Liberia, Belize, The Dominican Republic, Ecuador, El Salvador, Colombia, Peru, Haiti, Honduras and Nicaragua. However, the fluid based products are sold in liters and its multiples and submultiples.

The Imperial gallon is used in the British Virgin Island, Antigua and Barbuda, Anguilla, Dominica, Grenada, Bahamas, St. Vincent & the Grenadines, St. Lucia and the Cayman Island.

However, in Turks and Caicos Islands both the Imperial gallon and US gallon ius used due to the increase in tax duties disguised by levying the same duty on the 3.79 L US gallon as it was previously levied on the 4.55 L Imperial gallon.

How much does one gallon of water weigh?

One gallon (US) of water weighs 8.34 lbs or 3.78 kg at 62 °F (17 °C). An imperial gallon (UK) weighs 10.022 lbs or 4.546 kg, at its most dense temperature, which is 2.20456 lbs / L at 4 °C or 39 °F.

Different units of Gallon

There are three different units of gallon among which US has two definitions of gallon; the US liquid gallon and the US dry gallon and the other definition is in the form of UK gallon or the imperial gallon.

The US liquid gallon

The US liquid gallon is the most commonly used measuring unit, which is defined as the 231 cubic inches or 3.785 liters and weighs 8.344 lbs at its highest density. The expansion and contraction of arises with the rise in temperature while using the gallon for the trade purposes. For an example, according to the US government regulation the volume of both alcoholic beverages and petroleum products are used with reference to 600  F.

The US dry gallon

The US dry gallon is defined as 1/8th of a US bushel, which is 268.8025 cubic inches or 4.405 L. The weight of a US dry gallon is 9.711 lbs of water at its highest density. The US dry gallon is not used in the commercial purposes. However, it not even listed in the relevant statue which jumps from the dry quart to the peck.

The UK gallon or Imperial gallon

The UK gallon or imperial gallon originally was defined as 10 lbs of water, but the modern definition is exactly 4.54609 L or 10.02 lbs of water at its maximum density.

The effect of water temperature on the weight

The density of cold water is much higher than the ice, warm water and the liquid which is just above the freezing point. Water has the maximum density at 40C. his is an unusual property of the substance, resulting from hydrogen bonding. Therefore, a gallon of warm water would weighs slightly less than a gallon of cold water. The exact difference would depend on the temperatures, but it does not affects the value by much. However, the gravity effects weight of the liquid too. The weight of water is much more higher in Jupiter than that of Earth but it will be weight on moon than that of earth.

How US gallons are different to the imperial gallon?

One US gallon is equivalent to the 128 fluid ounces or 3.785 liters (US spelling) but in UK, the imperial gallon is equivalent to the 160 fluid ounces or 4.546 litres (UK spelling). The difference between the US Gallon and Imperial Gallon of UK is about 20 percent and has always led to confusion. The British adopted the measure of Imperial gallon in 1824, which is based on the calculation of 10 pounds or 277.42 cubic inches of water. The Americans had adopted the system where one gallon comprises of 231 inches of water. Therefore, the US gallon is 83.3 percent of the Imperial gallon of UK. However. If we put it another way the Imperial gallon of UK is about one-fifth or 20 percent greater in volume than the US gallon.