Litre: Difference between revisions

The litre (spelled litre in Commonwealth English and liter in American English) is a unit of capacity. There are two official symbols: lowercase l and uppercase L. The litre is a metric unit but not an SI unit though is accepted for use with the SI. The SI unit of volume is the cubic metre (m³).

Definitions and Equivalents

1 L (litre) ≡ 1/1000 m³ ≡ 1 dm³ (cubic decimetre) ≡ 1000 cm³ (cubic centimetres)

Practical SI multiples

In practical use only some of the SI unit prefixes are used with the litre unit.

Multiple	Name	Symbols			Multiple	Name	Symbols
100	litre	l	L
101	decalitre	dal	daL		10–1	decilitre	dl	dL
102	hectolitre	hl	hL		10–2	centilitre	cl	cL
103	kilolitre	kl	kL		10–3	millilitre	ml	mL
106	megalitre	Ml	ML		10–6	microlitre	µl	µL
109	gigalitre	Gl	GL		10–9	nanolitre	nl	nL
1012	teralitre	Tl	TL		10–12	picolitre	pl	pL
1015	petalitre	Pl	PL		10–15	femtolitre	fl	fL
					10–18	attolitre	al	aL

Name origin

The word "litre" is derived from an older French unit, the litron, whose name came from Greek via Latin.

Other common metric equivalencies

• 1 µL (microlitre) = 1 mm³ (cubic millimetre)

Conversions

One litre

≈ 0.87987699 Imperial quart

Inverse: One Imperial quart ≡ 1.1365225 litres

≈ 1.056688 US fluid quarts

Inverse: One US fluid quart ≡ 0.946352946 litres

≈ 0.0353146667 cubic foot

Inverse: One cubic foot ≡ 28.316846592 litres

One millilitre

≈ 0.03519507972785404600 Imperial fluid ounce

Inverse: One Imperial fluid ounce ≡ 28.4130625 mL

≈ 0.0338140227018429971686 US fluid ounce

Inverse: One US fluid ounce ≡ 29.5735295625 mL

≈ 0.0000353146667 cubic foot

Inverse: One cubic foot ≡ 28,316.846592 mL

Explanation

Litres are most commonly used for items measured by the capacity or size of their container (such as fluids and berries), 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 weighs almost exactly one kilogram. Similarly: 1 ml of water weighs about 1 g; 1000 litres of water weighs about 1000 kg (1 tonne). This relationship is due to the history of the unit but since 1964 has not been part of the definition.

Symbol

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, 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. On some typewriters, particularly older ones, the l key had to be used to type the numeral 1. Further, in some typefaces the two characters are nearly indistinguishable. This caused some concern, especially in the medical community. As a result, L (uppercase letter L) was accepted as an alternative symbol for litre in 1979. The United States National Institute of Standards and Technology now recommends the use of the uppercase letter L, 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.

Prior to 1979, the symbol ℓ (script small l, U+2113), came into common use in some countries; for example, it was recommended by South African Bureau of Standards publication M33 in the 1970s. This symbol can still be encountered occasionally in some English-speaking countries, but it is not used in most countries and not officially recognised by the BIPM, the International Organization for Standardization, or any national standards body.

History

In 1793, 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 litre was once again defined in exact relation to the metre, as another name for the cubic decimetre, that is, exactly 1 dm³. NIST Reference

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.

See also

• Claude Émile Jean-Baptiste Litre
• Pint
• Gallon
• Kilogram
• Cubic metre

External links

• BIPM's "SI Brochure"
• BIPM's "(Table 6 -) Non-SI units accepted for use with the International System"
• NIST note on SI units
• NIST recommends uppercase letter L
• UK National physical laboratory's "Internationally recognised non SI units" page