The original Frenchmetric system used the litre as abase unit. The wordlitre is derived from an older French unit, thelitron, whose name came from ByzantineGreek—where it was a unit of weight, not volume[2]—via Late Medieval Latin, and which equalled approximately 0.831 litres. The litre was also used in several subsequent versions of the metric system and is accepted for use with the SI,[3] although not anSI unit—the SI unit of volume is thecubic metre (m3). The spelling used by theInternational Bureau of Weights and Measures is "litre",[3] a spelling which is shared by most English-speaking countries. The spelling "liter" is predominantly used inAmerican English.[a]
One litre of liquid water has amass of almost exactly onekilogram, because the kilogram was originally defined in 1795 as the mass of one cubic decimetre of water at the temperature of melting ice (0 °C).[4] Subsequent redefinitions of the metre and kilogram mean that this relationship is no longer exact.[5]
Some SI units of volume to scale and approximate corresponding mass of water
A litre is a cubicdecimetre, which is the volume of a cube 10 centimetres × 10 centimetres × 10 centimetres (1 L ≡ 1 dm3 ≡ 1000 cm3). Hence 1 L ≡ 0.001 m3 ≡ 1000 cm3; and 1 m3 (i.e. a cubic metre, which is theSI unit for volume) is exactly 1000 L.
From 1901 to 1964, the litre was defined as the volume of one kilogram of pure water at maximum density (+3.98 °C)[citation needed] andstandard pressure. The kilogram was in turn specified as the mass of theInternational Prototype of the Kilogram (a specific platinum/iridium cylinder) and was intended to be of the same mass as the 1 litre of water referred to above. It was subsequently discovered that the cylinder was around 28 parts per million too large and thus, during this time, a litre was about1.000028 dm3. Additionally, the mass–volume relationship of water (as with any fluid) depends on temperature, pressure, purity and isotopic uniformity. In 1964, the definition relating the litre to mass was superseded by the current one. Although the litre is not an SI unit, it is accepted by theCGPM (the standards body that defines the SI) for use with the SI. CGPM defines the litre and its acceptable symbols.
A litre is equal in volume to themillistere, an obsolete non-SImetric unit formerly customarily used fordry measure.
Litres are most commonly used for items (such asfluids and solids that can be poured) 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 amass of almost exactly onekilogram when measured at its maximal density, which occurs at 3.984 °C. It follows, therefore, that1/1000 of a litre, known as one millilitre (1 mL), of water has a mass of about 1 g, while 1000 litres of water has a mass of about 1000 kg (1 tonne or megagram).
This relationship holds 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, with pressure.
It is now known that the density of water also depends on the isotopic ratios of the oxygen and hydrogen atoms in a particular sample. Modern measurements ofVienna Standard Mean Ocean Water, which is pure distilled water with anisotopic composition representative of the average of the world's oceans, show that it has a density of0.999975±0.000001 kg/L at its point of maximum density (3.984 °C) under one standard atmosphere (101.325 kPa) of pressure.[6]
The litre, though not an official SI unit, may be used withSI prefixes. The most commonly used derived unit is the millilitre, defined as one-thousandth of a litre, and also often referred to by the SI derived unit name "cubic centimetre". It is a commonly used measure, especially in medicine, cooking and automotive engineering. Other units may be found in the table below, where the more often used terms are in bold. However, some authorities advise against some of them; for example, in the United States,NIST advocates using the millilitre or litre instead of the centilitre.[7] There are two international standard symbols for the litre: L and l. In the United States the former is preferred because of the risk that (in some fonts) the letterl and thedigit1 may be confused.[8]
Amnemonic for its volume relative to an imperial pint is "a litre of water's a pint and three-quarters"; this is very close, as a litre is about 1.760 imperial pints.
A cubic foot has a volume of exactly28.316846592 L.
Originally, the only symbol for the litre wasl (lowercase letter L), following theSI convention that only those unit symbols that abbreviate the name of a person start with a capital letter. In many English-speaking countries, however, the most common shape of a handwrittenArabic digit 1 is just avertical stroke; that is, it lacks the upstroke added in many other cultures. Therefore, the digit "1" may easily be confused with the letter"l". In some computer typefaces, the two characters are barely distinguishable. As a result,L (uppercase letter L) was adopted by theCIPM as an alternative symbol for litre in 1979.[9] TheUnited StatesNational Institute of Standards and Technology now recommends the use of the uppercase letter L,[10] a practice that is also widely followed inCanada andAustralia. In these countries, the symbol L is also used with prefixes, as in mL and μL, instead of the traditional ml and μl used in Europe. Inthe UK andIreland, as well as the rest of Europe, lowercasel is used with prefixes, though whole litres are often written in full (so, "750 ml" on a wine bottle, but often "1 litre" on a juice carton). In 1990, theInternational Committee for Weights and Measures stated that it was too early to choose a single symbol for the litre.[11]
Prior to 1979, the symbol ℓ came into common use in some countries;[citation needed] for example, it was recommended bySouth African Bureau of Standards publication M33 and Canada in the 1970s. This symbol can still be encountered occasionally in some English-speaking and European countries like Germany, and its use is ubiquitous in Japan and South Korea.[citation needed]
Fonts covering theCJK characters usually include not only the script small ℓ but also four precomposed characters: ㎕, ㎖, ㎗, and ㎘ for the microlitre, millilitre, decilitre and kilolitre to allow correct rendering for vertically written scripts. These haveUnicode equivalents for compatibility, which are not recommended for use with new documents:[12]
U+2113ℓSCRIPT SMALL L
U+3395㎕SQUARE MU L
U+3396㎖SQUARE ML
U+3397㎗SQUARE DL
U+3398㎘SQUARE KL
TheCJK Compatibility block also includesU+3351㍑SQUARE RITTORU corresponding toリットルrittoru, Japanese for 'litre'.
The litre was introduced inFrance in 1795 as one of the new"republican units of measurement" and defined as onecubic decimetre.[14]One litre of liquid water has amass of almost exactly onekilogram, due to the gram being defined in 1795 as one cubic centimetre of water at the temperature of melting ice.[4]The original decimetre length was 44.344lignes, which was revised in 1798 to 44.3296lignes. This made the original litre1.000974 of today's cubic decimetre. It was against this litre that the kilogram was constructed.
In 1879, theCIPM adopted the definition of the litre, with the symboll (lowercase letter L).
In 1901, at the 3rdCGPM conference, the litre was redefined as the space occupied by 1 kg of purewater at the temperature of its maximum density (3.98 °C) under a pressure of 1 atm. This made the litre equal to about1.000028 dm3 (earlier reference works usually put it at1.000027 dm3).
In 1964, at the 12thCGPM 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.[5]
In 1979, at the 16thCGPM conference, the alternative symbolL (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.[11]
In spoken English, the symbol "mL" (for millilitre) can be pronounced as "mil". This can potentially cause confusion with some other measurement words such as:
"mm" formillimetre, a unit of length equal to one-thousandth of a metre
The abbreviation "cc" (forcubic centimetre, equal to a millilitre or mL) is a unit of thecgs system, which preceded theMKS system, which later evolved into theSI system. The abbreviation "cc" is still commonly used in many fields, including medical dosage and sizing forcombustion enginedisplacement.
The microlitre (μL) has been known in the past as thelambda (λ), but this usage is now discouraged.[15] In the medical field the microlitre is sometimes abbreviated asmcL on test results.[16]
In theSI system, apart from prefixes for powers of 1000, use of the "centi" (10−2), "deci" (10−1), "deca" (10+1) and "hecto" (10+2) prefixes with litres is common. For example, in many European countries, the hectolitre is the typical unit for production and export volumes ofbeverages (milk, beer, soft drinks, wine, etc.) and for measuring the size of the catch and quotas for fishing boats; decilitres are common inCroatia,Switzerland andScandinavia and often found in cookbooks, and restaurant and café menus; centilitres indicate the capacity of drinking glasses and of small bottles. In colloquialDutch inBelgium, a "vijfentwintiger" and a "drieëndertiger" (literally "twenty-fiver" and "thirty-threer") are the common beer glasses, the corresponding bottles mention 25 cL and 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.[citation needed] Similarly, alcoholshots are often marked in cL in restaurant menus, typically 3 cL (1.06 imp fl oz; 1.01 US fl oz).
In countries where the metric system was adopted as the official measuring system after theSI standard was established, common usage eschews prefixes that are not powers of 1000. For example, inCanada,Australia, andNew Zealand, consumer beverages are labelled almost exclusively using litres and millilitres. An exception is in pathology, where for instanceblood lead level[17] andblood sugar level[18] may be measured in micrograms/milligrams per decilitre.
For larger volumes, kilolitres, megalitres, and gigalitres, have been used by theNorthern Territory Government for measuring water consumption, reservoir capacities and river flows,[19] althoughcubic metres are also used. Cubic metres are generally used for non-liquid commodities, such as sand and gravel, or storage space.
^ab"Décret relatif aux poids et aux mesures du 18 germinal an 3 (7 avril 1795)" [Weights and measures decree dated 18 Germinal, Year 3 (7 April 1795)] (in French). Association Métrodiff. 7 April 1795. Archived fromthe original on 17 August 2016. Retrieved8 December 2012.Gramme, le poids absolu d'un volume d'eau pure égal au cube de la centième partie du mètre, et à la température de la glace fondante. English translation: "Gramme: the absolute weight of a volume of pure water equal to the cube of the hundredth part of the metre, at the temperature of melting ice."
^"Décret relatif aux poids et aux mesures du 18 germinal an 3 (7 avril 1795)" [Weights and measures decree dated 18 Germinal, Year 3 (7 April 1795)] (in French). Association Métrodiff. 7 April 1795. Archived fromthe original on 17 August 2016. Retrieved8 December 2012.Litre, la mesure de capacité, tant pour les liquides que pour les matières sèches, dont la contenance sera celle du cube de la dixièrne partie du mètre. English translation: "Litre: unit of capacity for both liquids and solids which will be equivalent to a cube of [with sides] one tenth of a metre."
Table 6 (Non-SI units accepted for use with the International System). Retrieved 2008-08-24
National Institute of Standards and Technology (11 November 2000)."Appendix C: General tables of units of measurement".NIST Handbook 44: Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. National Institute of Standards and Technology. Archived fromthe original on 10 December 2011. Retrieved9 October 2006.
Taylor, B.N. and Thompson, A. (Eds.). (2008a).The International System of Units (SI)Archived 3 June 2016 at theWayback Machine. United States version of the English text of the eighth edition (2006) of the International Bureau of Weights and Measures publicationLe Système International d' Unités (SI) (Special Publication 330). Gaithersburg, MD: National Institute of Standards and Technology. Retrieved 2008-08-18.
