Convert Liters to Gallons

Liter - The litre or liter (see spelling differences) is a unit of volume. There are two official symbols: the Latin letter L in lower and upper case (l and L). The lower case L is also often written as a cursive l, though this symbol has no official approval by any international bureau. Although the litre is not an SI unit, it is accepted for use with the SI, and has appeared in several versions of the metric system. The official SI unit of volume is the cubic metre (m3). One litre is equal to 0.001 cubic metre and is denoted as 1 cubic decimetre (dm3). The word litre is derived from an older French unit, the litron, whose name came from Greek via Latin. The original French metric system used the litre as a base unit. The spelling of the word used by the International Bureau of Weights and Measures is "litre". This spelling is also the usual one in English in most English speaking countries, but the usual American English spelling is "liter", which is officially endorsed by the United States.

Litres are most commonly used for items (such as fluids and berries) which are measured by the capacity or size of their container, whereas cubic metres (and derived units) are most commonly used for items measured either by their dimensions or their displacements. The litre is often also used in some calculated measurements, such as density (kg/L), allowing an easy comparison with the density of water. One litre of water has a mass of almost exactly one kilogram when measured at its maximal density, which occurs at about 4 degrees Celsius. Similarly: 1 millilitre of water has about 1 g of mass; 1,000 litres of water has about 1,000 kg of mass. This relationship is because the gram was originally defined as the mass of 1 mL of water. However, this definition was abandoned in 1799 because the density of water changes with temperature and, very slightly, pressure.

In 1795, the litre was introduced in France as one of the new "Republican Measures", and defined as one cubic decimetre. In 1879, the CIPM adopted the definition of the litre, and the symbol l (lowercase letter L). In 1901, at the 3rd CGPM conference, the litre was redefined as the space occupied by 1 kg of pure water at the temperature of its maximum density (3.98 °C) under a pressure of 1 atm. This made the litre equal to about 1.000 028 dm3 (earlier reference works usually put it at 1.000 027 dm3). In 1964, at the 12th CGPM conference, the original definition was reverted to, and thus the litre was once again defined in exact relation to the metre, as another name for the cubic decimetre, that is, exactly 1 dm3. In 1979, at the 16th CGPM conference, the alternative symbol L (uppercase letter L) was adopted. It also expressed a preference that in the future only one of these two symbols should be retained, but in 1990 said it was still too early to do so.

In spoken English, the abbreviation "mL" (for millilitre) is often pronounced as "mil", which is homophonous with the colloquial term "mil", which is intended to mean "one thousandth of a metre". This generally does not create confusion, because the context is usually sufficient - one being a volume, the other a linear measurement. The colloquial use of "mil" for millimetre for an ambiguous topic as in "5 mils of rain fell since 9am" may, however, be confusing. And in the United States a term of the same spelling and pronunciation means a thousandth of an inch.

The abbreviation cc (for cubic centimetre, equal to a millilitre or mL) is a unit of the cgs system, that preceded the MKS system, that later evolved into the SI system. The abbreviation cc is still commonly used in many fields including (for example) sizing for motorcycle and related sports for small combustion engine displacement; larger engines, such as automobile engines, do have their displacement measured in litres.

In European countries where the metric system was established well before the adoption of the SI standard, there is still carry-over of usage from the precursor cgs and MKS systems. In the SI system, use of prefixes for multiples of 1,000 is preferred and all other multiples discouraged. However, in countries where these other multiples were already established, their use remains common. In particular, use of the centi (10-2), deci (10-1), deca (10+1), and hecto (10+2) prefixes are still common. For example, in many European countries, the hectolitre is the typical unit for production and export volumes of beverages (milk, beer, soft drinks, etc) and for measuring the size of the catch and quotas for fishing boats; decilitres are found in cookbooks; centilitres indicate the capacity of drinking glasses and of small bottles. In colloquial Dutch in Belgium, a 'vijfentwintiger' and a 'drieendertiger' (literally 'twenty-fiver' and 'thirty-threer') are the common beer glasses, the corresponding bottles mention 25 cL or 33 cL. Bottles may also be 75 cL or half size at 37.5 cL for 'artisanal' brews or 70 cL for wines or spirits. Cans come in 25 cL, 33 cL and 50 cL aka 0.5 L. Family size bottles as for soft drinks or drinking water use the litre (0.5 L, 1 L, 1.5 L, 2 L), and so do beer barrels (50 L, or the half sized 25 L). This unit is most common for all other household size containers of liquids, from thermocans, by buckets, to bath tubs; as well as for fuel tanks and consumption for heating or by vehicles.

In countries where the metric system was adopted as the official measuring system after the SI standard was established, common usage more closely follow contemporary SI conventions. For example, in Canada where the metric system is now in widespread use, consumer beverages are labelled almost exclusively using litres and millilitres. Hectolitres sometimes appear in industry, but centilitres and decilitres are rarely, if ever, used. Larger volumes are usually given in cubic metres (equivalent to 1 kL), or thousands or millions of cubic metres. The situation is similar in Australia, although kilolitres, megalitres and gigalitres are commonly used for measuring water consumption, reservoir capacities and river flows. For larger volumes of fluids, such as annual consumption of tap water, lorry (truck) tanks, or swimming pools, the cubic metre is the general unit, as it is generally for all volumes of a non-liquid nature.

Gallon - A gallon is a measure of volume of approximately four litres. Historically it has had many different definitions, but there are three definitions in current use. These are the U.S. liquid gallon (approx. 3.8 litres) and the U.S. dry gallon (approx. 4.4 L) which are in use in the United States, and the Imperial (UK) gallon (approx. 4.5 L) which is in unofficial use within the United Kingdom. One or other version is sometimes found in other English-speaking countries.

The U.S. liquid gallon is legally defined as 231 cubic inches, and is equal to exactly 3.785 411 784 litres (1 L = 10-3 m3) or 0.133 680 555... cubic feet. This is the most common definition of a gallon in the United States. The U.S. fluid ounce is defined as 1/128 of a U.S. gallon. The U.S. dry gallon is one-eighth of a U.S. Winchester bushel of 2150.42 cubic inches, thus it is equal to exactly 268.8025 cubic inches or 4.404 883 770 86 litres. The U.S. dry gallon is less commonly used, and is not listed in the relevant statute, which jumps from the dry quart to the peck. The Imperial (UK) gallon was legally defined as 4.546 09 litres. This definition is used in some Commonwealth countries and Ireland, and is based on the volume of 10 pounds of water at 62 °F. (A U.S. liquid gallon of water weighs about 8.33 pounds at the same temperature.) The Imperial fluid ounce is defined as 1/160 of an Imperial gallon. As of 1 January 2000 it ceased to be legal within the United Kingdom for economic, health, safety or administrative purposes.

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 18.5 inches in diameter and 8 inches depth. That made the dry gallon 268.80252 cubic inches. 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 268.8025 cubic inches exactly (4.40488377086 L). In previous centuries there had been a corn gallon of around 271 to 272 cubic inches.

The wine, fluid, or liquid gallon is 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. 230.90706 cubic inches. It had been redefined during the reign of Queen Anne, in 1706, as 231 cubic inches exactly (3 x 7 x 11 in), which is the result of the earlier definition with pi approximated to 22/7. 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 gallon is 1369:1176, but 268.8:231 is exactly 64:55 or ca. 13:11. This approximation is still applicable, although the ratio of 1.164115646 slightly changed to 1.163647186 with current definitions (268.8025:231 = 107521:92400, approx. 1351:1161). In some contexts it is or was necessary to disambiguate between those two U.S. gallons, so "liquid" or "fluid" and "dry" respectively are then added to the name.

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 0.998859 grams per millilitre weighed in air of density 0.001217 g/mL against weights of density 8.136 g/mL. This works out at approximately 4.5460903 L (277.4416 cu in). The metric definition of exactly 4.54609 cubic decimetres (also 4.54609 L after the litre was redefined in 1964, ca. 277.419433 cu in) was adopted shortly afterwards in Canada; for several years, the conventional value of 4.546092 L 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.