3.2 Litre
Hedvig Horning
One litre of liquid water has a mass of almost exactly one kilogram, 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]
Litres are most commonly used for items (such as fluids 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 a mass of almost exactly one kilogram when measured at its maximal density, which occurs at about 4 C. It follows, therefore, that 1000th of a litre, known as one millilitre (1 mL), of water has a mass of about 1 g; 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 of Vienna Standard Mean Ocean Water, which is pure distilled water with an isotopic composition representative of the average of the world's oceans, show that it has a density of 0.9999750.000001 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 with SI 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 letter l and the digit 1 may be confused.[8]
One litre is slightly larger than a US liquid quart and slightly less than an imperial quart or one US dry quart. A mnemonic 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 1.76 imperial pints.
Originally, the only symbol for the litre was l (lowercase letter L), following the SI 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 handwritten Arabic digit 1 is just a vertical 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 the CIPM as an alternative symbol for litre in 1979.[9] The United States National Institute of Standards and Technology now recommends the use of the uppercase letter L,[10] a practice that is also widely followed in Canada and Australia. 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. In the UK and Ireland, as well as the rest of Europe, lowercase l 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, the International Committee for Weights and Measures stated that it was too early to choose a single symbol for the litre.[11]
The litre was introduced in France in 1795 as one of the new "republican units of measurement" and defined as one cubic decimetre.[14]One litre of liquid water has a mass of almost exactly one kilogram, 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 44.344 lignes, which was revised in 1798 to 44.3296 lignes. This made the original litre 1.000974 of today's cubic decimetre. It was against this litre that the kilogram was constructed.
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 1.000028 dm3 (earlier reference works usually put it at 1.000027 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.[5]
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.[11]
The abbreviation "cc" (for cubic centimetre, equal to a millilitre or mL) is a unit of the cgs system, which preceded the MKS system, which later evolved into the SI system. The abbreviation "cc" is still commonly used in many fields, including medical dosage and sizing for combustion engine displacement.
The microlitre (μL) has been known in the past as the lambda (λ), but this usage is now discouraged.[15] In the medical field the microlitre is sometimes abbreviated as mcL on test results.[16]
In countries where the metric system was adopted as the official measuring system after the SI standard was established, common usage eschews prefixes that are not powers of 1000. For example, in Canada, Australia, and New Zealand, consumer beverages are labelled almost exclusively using litres and millilitres. An exception is in pathology, where for instance blood lead level[17] and blood sugar level[18] may be measured in micrograms/milligrams per decilitre.
For larger volumes, kilolitres, megalitres, and gigalitres, have been used by the Northern Territory Government for measuring water consumption, reservoir capacities and river flows,[19] although cubic metres are also used. Cubic metres are generally used for non-liquid commodities, such as sand and gravel, or storage space.
One litre is the volume of 1000 cubic centimetres, that is a cube of 10 10 10 centimetres (1000 cm3). One litre of water at 4 C (277 K; 39 F) has the mass of exactly one kilogram. This results from the definition given in 1795, where the gram was defined as the weight of one cubic centimetre of melting ice.[2]
The metric system was first introduced in France in 1791.[3][4] That system did not have its own unit of capacity or volume because volume can be measured in cubic metres.[4] In 1793 work to make the metric system compulsory in France was started by the Temporary Commission of Republican Weights and Measures. Due to public demand,[4] the commission said that the cubic metre was too big for everyday use. They said that a new unit based on the old cadil should be used instead. One cadil was to be 0.001 cubic metres. This was equivalent to a cube with sides 10 cm.[5] The cadil was also known as the pinte or the litron. The pinte had been an old French unit of measure of capacity.[4] In 1795 the definition was revised. The cadil was given the name litre.[6]
In 1795 the kilogram was defined to be exactly one litre of water at 4 C. In 1799 the kilogram was redefined. The new definition said that the kilogram was the mass of the kilogram des archives. In 1901 scientists measured the volume of one litre of water at 4 C very carefully.[Note 1] They found that it occupied about 1.000028 dm3.[7] The BIPM redefined the litre as being exactly the volume of one kilogram of water at 4 C.[8]
In 1960 the SI was introduced. The BIPM changed the definition of the litre back to "one dm3". The litre is not part of SI. The BIPM defined the litre[Note 2] as a "Non-SI unit accepted for use with the SI". This was because it is used in many countries. The BIPM said that the litre should not be used for very accurate work.[9][10]
According to SI rules, the symbol for the litre should be "l". This is because the litre was not named after somebody whose name was "Litre".[Note 3] However the symbol "l" and the number "1" are easily confused. In 1979 the BIPM made an exception for the symbol for the litre. They said that people could use either "L" or "l" as its symbol.[11]
We track motor fuel prices across Ontario and report our findings. The rates on this page (listed in Canadian cents per litre) are gathered weekly and published every Monday. They reflect full- and self-serve retail prices for various fuel types, including taxes.
Prices are made up of various components, shown here for regular unleaded gasoline in Toronto and Thunder Bay. In , the average pump price in Toronto was cents per litre and the average pump price in Thunder Bay was . Note: crude oil costs are estimated based on supply from Western Canada.
The federal government proposes to further increase the carbon tax on gasoline beyond 2023 by about 3.3 cents per litre each year (on April 1st) to 37.43 cents per litre in 2030. It is not part of the wholesale price of gasoline, but is subject to HST and is reflected in the retail price. The federal carbon tax is now 17.57 cents per litre.
In 2018, Ontario cancelled the provincial cap-and-trade program, which had increased the price of gasoline by about 4.3 cents per litre. On September 7, 2018 it was removed from wholesale gasoline prices in Ontario.