Editing Kilo-

{{Short description|Decimal unit prefix in the metric system}}
{{Other uses|Kilo (disambiguation){{!}}Kilo}}
{{Wiktionary|kilo-}}

'''Kilo''' is a [[decimal prefix|decimal]] [[metric prefix|unit prefix]] in the [[metric system]] denoting multiplication by one [[thousand]] (10<sup>3</sup>). It is used in the [[International System of Units]], where it has the symbol '''k''', in [[Letter case|lowercase]].

The prefix ''kilo'' is derived from the [[Greek language|Greek]] word {{lang|el|χίλιοι}} ({{lang|el-Latn|chilioi}}), meaning "thousand". 

In 19th century English it was sometimes spelled chilio, in line with a [[Linguistic purism|puristic]] opinion by [[Thomas Young (scientist)|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 [[gram]]s
* one [[kilometre]] (km) is 1000 [[metre]]s
* one [[kilojoule]] (kJ) is 1000 [[joule]]s
* one kilolitre (kL) is 1000 [[litre]]s
* one kilobaud (kBd) is 1000 [[baud]]s
* one kilohertz (kHz) is 1000 [[hertz]]
* one kilodalton (kDa) is 1000 [[Dalton (unit)|daltons]]
* one [[kilobit]] (kb) is 1000 [[bit]]s
* one [[kilobyte]] (kB) is 1000 [[byte]]s
* one kiloohm is (kΩ) is 1000 [[ohm]]s
* one [[kilosecond]] (ks) is 1000 [[Second|seconds]]
*one [[kilotonne]] (kt) is 1000 [[Tonne|tonnes]]

By extension, currencies are also sometimes preceded by the prefix kilo-:
* one kiloeuro (k€) is 1000 [[euro]]s
* one kilodollar (k$) is 1000 [[dollar]]s

==kilobyte==
For the kilobyte, a second definition has been in common use in some fields of [[computer science]] and information technology. It uses ''kilobyte'' to mean 2<sup>10</sup> bytes (= 1024 bytes), because of the [[Mathematical coincidence#Concerning base 2|mathematical coincidence]] that 2<sup>10</sup> is approximately 10<sup>3</sup>. The reason for this application is that digital hardware and architectures natively use [[base 2]] exponentiation, and not [[base 10|decimal]] systems. [[JEDEC memory standards]] still permit this definition, but acknowledge the correct SI usage.

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", instead of kilo for 1024.<ref>[http://physics.nist.gov/cuu/Units/binary.html Definition of binary prefixes at NIST]</ref>  To address this conflict, a new set of [[binary prefix]]es has been introduced, which is based on powers of 2. Therefore, 1024 bytes are defined as one [[kibibyte]] (1 KiB).

==Exponentiation==
When units occur in [[exponentiation]], such as in square and cubic forms, any multiplier prefix is considered part of the unit, and thus included in the exponentiation.
* 1&nbsp;km<sup>2</sup> means one square kilometre or the area of a [[Square (geometry)|square]] that measures 1000&nbsp;m on each side or 10<sup>6</sup>&nbsp;m<sup>2</sup> (as opposed to 1000 square meters, which is the area of a square that measures 31.6&nbsp;m on each side).
* 1&nbsp;km<sup>3</sup> means one cubic kilometre or the volume of a [[cube]] that measures 1000&nbsp;m on each side or 10<sup>9</sup>&nbsp;m<sup>3</sup> (as opposed to 1000 cubic meters, which is the volume of a cube that measures 10&nbsp;m on each side).

==See also==
* [[milli-]] (inverse of kilo- prefix, 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)]]

[[he:תחיליות במערכת היחידות הבינלאומית#קילו]]