Editing Litre (section)

==Explanation==

Litres are most commonly used for items (such as [[fluid]]s 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 3.984&nbsp;°C. It follows, therefore, that {{sfrac|1000}} of a litre, known as one millilitre (1 mL), of water has a mass of about 1&nbsp;g, while 1000&nbsp;litres of water has a mass of about 1000&nbsp;kg (1&nbsp;[[tonne]] or megagram).

This relationship holds because the gram was originally defined as the mass of 1&nbsp;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 [[Isotope|isotopic]] composition representative of the average of the world's oceans, show that it has a density of {{val|0.999975|0.000001|u=kg/L}} at its point of maximum density (3.984&nbsp;°C) under one standard atmosphere (101.325&nbsp;[[Pascal (unit)|kPa]]) of pressure.<ref>Isotopic composition and temperature per London South Bank University's [http://www1.lsbu.ac.uk/water/data.html "List of physicochemical data concerning water"], density and uncertainty per [http://webbook.nist.gov/chemistry/ NIST Standard Reference Database Number 69] (Retrieved: 2010-04-05).</ref>