<P> A litre of water has a mass almost exactly equal to one kilogram . An early definition of the kilogram was set as the mass of one litre of water . Because volume changes with temperature and pressure, and pressure uses units of mass, the definition of a kilogram was changed . At standard pressure, one litre of water has a mass of 0.999975 kg at 4 ° C, and 0.997 kg at 25 ° C . </P> <P> 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". Further, on some typewriters, particularly older ones, the unshifted L key had to be used to type the numeral 1 . Even in some computer typefaces, the two characters are barely distinguishable . This caused some concern, especially in the medical community . </P> <P> As a result, L (uppercase letter L) was adopted 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 . 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 CIPM stated that it was still too early to choose a single symbol for the litre . </P> <P> 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 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 . Fonts covering the CJK characters usually include not only the script small l but also four precomposed characters: μl, ml, dl and kl (U + 3395 to U + 3398) for the microlitre, millilitre, decilitre and kilolitre . Such usage in printed works is in conflict with the recommendations published by the BIPM on the advice of the major international standards organisations (including ISO, NIST, NPL, IAU, IUPAC and IUPAP) who state in the SI Brochure that unit symbols should be "printed in Roman (upright) type regardless of the type used in the surrounding text". </P>

What is the difference between litres and kilograms