Liter

Cube 10 cm x 10 cm x 10 cm (1 liter)

The liter (symbols L or l) is a decimal metric unit of volume, accepted by the SI, equal to 1 cubic decimeter (dm³), 1000 cubic centimeters (cm³), or 1/1000 cubic meter. A cubic decimeter (or liter) occupies a volume of 10 cm × 10 cm × 10 cm (see figure) and is therefore equal to one thousandth of a cubic meter.

The original French metric system used the liter as the base unit. The word liter is derived from an older French unit, the litron, whose name comes from the Greek, (where it was a unit of weight, not volume) through from Latin, and which was equivalent to approximately 0.831 litres. The liter was also used in several later versions of the metric system and is accepted for use with the SI, even though it is not an SI unit, since the SI unit of volume is the cubic meter (m³).

A liter 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 decimeter of water at the melting temperature of ice. Subsequent redefinitions of the meter and kilogram mean that this relationship is no longer exact.

Definition

Maßkrüge, one-liter beer jars, during the 2006 Oktoberfest in Germany

A liter is defined as a special name for a cubic decimeter or 10 centimeters × 10 centimeters × 10 centimeters, (1 L ≡ 1 dm³ ≡ 1000 cm³). Therefore 1 L ≡ 0.001 m³ ≡ 1000 cm³, and 1 m³ (that is, one cubic meter, which is the SI unit for volume) is exactly 1000 L.

From 1901 to 1964, the liter was defined as the volume of one kilogram of pure water at its maximum density and standard pressure. The kilogram was itself specified as the mass of a platinum/iridium cylinder kept at Sèvres in France, and was assumed to have the same mass as a liter of water, as mentioned above. The cylinder was later found to be about 28 parts per million larger, and therefore during this time a liter was about 1,000028 dm³. Furthermore, the mass-volume relationship of water (like that of any fluid) depends on temperature, pressure, purity, and isotopic uniformity. In 1964, the definition of a liter that referred to mass was abandoned in favor of the current one. Although the liter is not an SI unit, it is accepted by the CGPM (the standards body that defines the SI) for use with the SI, thus also defining the liter and its acceptable symbols.

A liter is equal in volume to a millistere, an obsolete non-SI metric unit commonly used to measure aggregates.

Explanation

Liters are most commonly used for products (fluid and pourable solids) that are measured by the capacity or size of their container, while cubic meters (and derived units) are more commonly used for measured items by their dimensions or their displacements. The liter is also used in some calculated measurements, such as density (kg/L), which allows for easy comparison with the density of water.

A liter of water has a mass of almost exactly one kilogram when measured at its maximum density, which occurs at about 4°C. Similarly: a milliliter (1 ml) of water has a mass of about 1 g; 1,000 liters of water have a mass of about 1,000 kg (1 ton). 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 the Vienna Standardized Mean Ocean Water, which is pure distilled water with an isotopic composition representative of the mean of the world's oceans, show it to have a density of 0.999975 ± 0.000001 kg/L at its point of maximum density (3.984 °C) under a standard atmosphere (760 Torr, 101.325 kPa) of pressure.

SI prefixes applied to the liter

Liter can be used with any SI prefix. The most frequently used is the milliliter, defined as one thousandth of a liter (one cubic centimeter) or hectoliter (one hundred liters) used by wine growers or industrial beer producers. Other units can be seen in the table, the most frequent in bold.

Conversion to non-metric units

Equivalences

Double decaliter (20 liters).

Vaso medidor con equivalence entre littro (marked "Ltr") and milliliters ("ml").

• 1000 mL

• 100 cL

• 10 dL

• 0.1 daL

• 0.01 hL

• 0.001 kL

Derived Units

• To measure the flow of liquids and gases the following units are used: liter per second (l/s), liter per minute (l/ min), liter per hour (l/h), as well as corresponding multiples and submultiplos.
• To measure the density and content (mass concentration) of the substances, units are used: gram per litre, kilogram per litre, milligram per litre and similar.
• To measure molar density and molar concentration of substances, units are used: mol per litre (mol/l), micromol/liter and similar.
• To measure the volumetric concentration of particles, a reciprocal litre (l -1) and derivatives (ml -1 μl -1 and similar) are used. Thus, a volume concentration of 100 μl −1 means that 1 microliter of any volume contains, on average, 100 particles.
• To measure the energy in some applications, a liter-atmosphere unit is used, which is equal to the work that the piston of a thermal machine produces on a gas at a constant pressure of 1 atmosphere (103125 Pa), compressing the gas with a volume decrease in 1 litre. 1 liter-atmosphere (l atm) = 101,325 J.
• To measure the absorption capacity of the sorbents the unit l/l (which expresses the ratio between the absorbed gas volume and the volume of the sorbent). This unit is sometimes used to measure porosity.
• To measure the specific surface area per volume unit of a porous substance or other dispersed system, a m2 / l unit is used.
• To measure the volumetric radiation of substances (usually air), the Bq / l unit (becquerel per liter) is used.

Rough Conversions

A liter is slightly larger than a "US liquid quart" and slightly smaller than an "Imperial quart" or "US dry quart". A mnemonic for its volume in relation to an imperial pint is "a liter of water is a pint and three-quarters"; this is very close, as one liter is actually 1.75975399 pints.

A liter is the volume of a cube 10 cm on a side, which is slightly less than a cube 4 inches on a side (one-third of a foot). One cubic foot would hold exactly 27 such cubes (four inches on a side), so one cubic foot is roughly equal to 27 liters. A cubic foot has an exact volume of 28.316846592 liters, which is 4.88% larger than the approximation of 27 liters.

A liter of liquid water has a mass almost exactly equal to a kilogram. One of the first definitions of the kilogram was stated as the mass of one liter of water. Since volume changes with temperature and pressure, and pressure uses units of mass, the definition of the kilogram has been changed. At standard pressure, a liter of water has a mass of 0.999975 kg at 4 °C, and 0.997 kg at 25 °C.

Symbol

Originally, the only symbol for liter was l (lowercase letter L), following the SI convention that only unit symbols that abbreviate a person's name start with a capital letter. However, in many English-speaking countries, the most common form of the handwritten Arabic digit 1 is simply a vertical stroke; that is, it lacks the oblique stroke added in many other cultures. Therefore, the digit "1" can easily be confused with the letter "l". Also, on some typewriters, particularly older ones, the lowercase L key was used to type the number 1. Even in some computer fonts, the two characters are barely distinguishable. This caused some concern, especially in the medical community.

As a result, L (capital letter L) was adopted as an alternate symbol for liter in 1979. The US National Institute of Standards and Technology now recommends the use of the capital letter L, a practice also widely followed in Canada and Australia. In these countries, the symbol L is also used with prefixes, such 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, the lowercase letter l is used with prefixes, although whole liters are often written in full (thus "750 ml » on a bottle of wine, but often «1 litre» on a juice container). In 1990, the CIPM declared that it was too early to choose a single symbol for the litre.

Before 1979, the symbol ℓ (lowercase italic l, U+2113), came into common use in some countries; for example, it was recommended by the South African standards body publication M33, and by Canada, in the 1970s. This symbol can still be found occasionally in some English-speaking and European countries such as Germany, and its use is ubiquitous in Japan and South Korea. Fonts that include CJK characters typically include not only the italic ℓ but also four precomposed characters: ㎕, ㎖, ㎗ and ㎘ (U+3395 to U+3398) for microliter, milliliter, deciliter, and kiloliter.

In 1979, the XVI General Conference on Weights and Measures adopted a decision, according to which, as an exception, the use of two different denominations of the liter is allowed: lowercase l and uppercase L. The US National Institute of Standards and Technology recommends the use of the symbol L for liters; this practice is also widespread in Canada and Australia. In these countries, the symbol L is also used with prefixes, for example mL and µL instead of the traditional ml and µl used in Europe. In the UK and Ireland, as in other European countries, a lower case letter (ml and µl) is used in conjunction with the prefixes and, in the case of whole litres, the word is usually written in its entirety (1 litre). In 1990, the International Committee for Weights and Measures announced that it was too early to choose a common symbol for the litre. Until 1979, the symbol ℓ (small letter l, U +2113) became widespread, for example, it was recommended by the South African and Canadian Bureau of Standards in 1970. Use of this symbol still survives small scale in English-speaking countries, while in Japan and South Korea it is used everywhere. Supporting FontsSouth Asian characters (English CJK characters) generally contain not only the character ℓ, but also four derived characters: ㎕, ㎖, ㎗, and ㎘ (U+3395 to U+3398) for microliters, milliliters, deciliters, and kiloliters, respectively. The use of these symbols in printed works contradicts the recommendations published by the International Bureau of Weights and Measures at the request of the main international standardization organizations (including ISO NIST IAU IUPAC IUPAP and NPL), which states that the symbols for the units they must “print in vertical type regardless of the font type of the surrounding text.”

History

The first name of the liter was "cadil"; the patterns are displayed in the Museum of Arts and Crafts in Paris.

The liter was introduced to France in 1795 as one of the new "republican units of measure" and was defined as a cubic decimeter. The original decimeter had a length of 44.344 lignes, which was revised in 1798 to 44.3296 lignes. This made the original liter 1,000974 cubic decimeters today. It was with this liter as a reference that the kilogram was defined.

In 1879, the CIPM adopted the definition of the liter, with the symbol l (small letter L).

In 1901, at the 3rd CGPM conference, the liter 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.

In 1964, at the 12th CGPM conference, the original definition was reversed, and thus the liter was once again defined in exact relation to the metre, as another name for the cubic decimeter, i.e. exactly 1 dm³.

In 1979, at the 16th CGPM conference, the alternative symbol L (capital letter L) was adopted.

The abbreviation cc (for cubic centimeter, equal to one milliliter or mL) is a unit of the CGS system, which preceded the MKS system, which later evolved into the YES system. The abbreviation cc is still commonly used in many fields, including medical dosing and sizing for small displacement combustion engines, such as those used in motorcycles.

The microliter (μL) has in the past been known as lambda (λ), but this usage is now discouraged. In the medical field, the microliter is sometimes abbreviated as mcL in the test results.

In the SI system, the use of prefixes for powers of 1000 is preferred and all other multiples are not recommended. However, in countries where the metric system was established long before the adoption of the SI standard, other multiples were already established, its use is still common. In particular, the use of the prefixes centi (10 ⁻²), deci (10 ⁻¹), deca (10 ⁺¹) and hecto (10 ⁺²) are still common. For example, in many European countries, the hectoliter is the typical unit for the production and export volumes of beverages (milk, beer, soft drinks, wine, etc.) and for measuring the size of catches. and fishing boat quotas; deciliters are common in Switzerland and Scandinavia and are sometimes found in cookbooks; centiliters indicate the capacity of glasses and small bottles. In colloquial Dutch in Belgium, a "vijfentwintiger" and a "drieëndertiger" (literally "twenty-eight" and "thirty-three") are the common beer glasses, the corresponding bottles quoting 25 cL or 33 cL. Bottles can also be 75 cL or "half bottle", 37.5 cL for 'artisanal' or 70 cL for wines or spirits. The cans come in 25 cL, 33 cL and 50 cL.

In countries where the metric system was adopted as the official measurement system after the SI standard was established, common usage more closely follows contemporary SI conventions. For example, in Canada, Australia, and New Zealand, consumer beverages are almost exclusively labeled with liters and milliliters. Hectoliters sometimes appear in industry, but centiliters and deciliters are rarely, if ever, used. An exception is pathology, where, for example, the blood lead level can be measured in micrograms per deciliter. Larger volumes are generally given in cubic meters (equivalent to 1 kL) or thousands or millions of cubic meters.

Although kiloliters, megaliters and gigaliters are commonly used to measure water consumption, reservoir capacity and flow rates, rivers, for larger volumes of liquids, such as annual consumption of tap water, tankers, or swimming pools, the cubic meter is the general unit. The same for all volumes of a non-liquid nature.

Use to indicate capacity

Fields where the liter and milliliter are used as a measure for non-liquid volumes, where the capacity of the container is indicated, include:

• Solid elements that can be poured and measured by their containers (such as, in many places, berries)
• The size of the trunk in the car industry
• Backpacks
• Computer boxes
• Microwave ovens
• Refrigerators
• Recycling container
• Cylinder