{{Short description|Decimal unit prefix in the metric system}} {{Other uses|Kilo (disambiguation){{!}}Kilo}} {{Wiktionary|kilo-}}
'''Kilo''' is a unit prefix in the metric system of measurement, denoting multiplication by one thousand (10<sup>3</sup>). The International System of Units reserves the lowercase symbol '''k'''.
''Kilo'' is derived from the Greek word {{lang|el|χίλιοι}} ({{lang|el-Latn|chilioi}}), meaning "thousand".
In 19th century English the prefix was sometimes spelled chilio, in line with a puristic opinion by Thomas Young.<ref name="Brewster_1832">{{cite book |title=The Edinburgh Encyclopaedia |first=David |last=Brewster |volume=12 |edition=1st American |date=1832 |publisher=Joseph and Edward Parker<!-- |printer=William Brows --> |url=https://books.google.com/books?id=17RGAQAAIAAJ&pg=PA572 |access-date=2015-10-09}}</ref><ref name="Dingler_1823">{{cite book |title=Polytechnisches Journal |first=Johann Gottfried |last=Dingler |volume=11 |date=1823 |publisher=J.W. Gotta'schen Buchhandlung |language=de |location=Stuttgart, Germany |url=https://books.google.com/books?id=wF3zAAAAMAAJ&pg=PA500 |access-date=2015-10-09}}</ref> As an opponent of suggestions to introduce the metric system in Britain, he qualified the nomenclature adopted in France as barbarous.
== Examples == * one kilogram (kg) is 1000 grams * one kilometre (km) is 1000 metres * one kilojoule (kJ) is 1000 joules * one kilolitre (kL) is 1000 litres * one kilobaud (kBd) is 1000 bauds * one kilohertz (kHz) is 1000 hertz * one kilodalton (kDa) is 1000 daltons * one kilobit (kb) is 1000 bits * one kilobyte (kB) is 1000 bytes * one kiloohm is (kΩ) is 1000 ohms * one kilosecond (ks) is 1000 seconds *one kilotonne (kt) is 1000 tonnes
By extension, currencies are sometimes also preceded by the prefix: * one kiloeuro (k€) is 1000 euros * one kilodollar (k$) is 1000 dollars
==kilobyte== For multiples of the byte in some fields of computer science and information technology, another definition has been in common use, in which the ''kilobyte'' measures 1024 bytes (2<sup>10</sup> bytes), because 2<sup>10</sup> is approximately 10<sup>3</sup>. The reason for this application is that digital hardware natively use base 2 exponentiation.
The National Institute of Standards and Technology (NIST) comments on the confusion caused by these contrasting definitions: "Faced with this reality, the ''IEEE Standards Board'' decided that IEEE standards will use the conventional, internationally adopted, definitions of the SI prefixes."<ref>[http://physics.nist.gov/cuu/Units/binary.html Definition of binary prefixes at NIST]</ref> A new set of binary prefixes, based on powers of 2, was introduced by the International Electrotechnical Commission (IEC), which defines 1024 bytes as one kibibyte (1 KiB).
==Exponentiation== When units occur in exponentiation, such as in square and cubic forms, any multiplier prefix is part of the unit, and thus included in the exponentiation. * 1 km<sup>2</sup> means one square kilometre or the area of a square that measures 1000 m on each side or 10<sup>6</sup> m<sup>2</sup> (as opposed to 1000 square meters, which is the area of a square that measures 31.6 m on each side). * 1 km<sup>3</sup> means one cubic kilometre or the volume of a cube that measures 1000 m on each side or 10<sup>9</sup> m<sup>3</sup> (as opposed to 1000 cubic meters, which is the volume of a cube that measures 10 m on each side).
==See also== * milli (inverse of kilo, denoting a factor of 1/1000) * kibi (binary prefix, denoting a factor of 1024) * RKM code
==References== {{reflist}}
{{SI prefixes (infobox)}}
Category:SI prefixes Category:1000 (number)