# Kilo-

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Decimal unit prefix in the metric system

For other uses, see [Kilo](/source/Kilo_(disambiguation)).

Look up ***[kilo-](https://en.wiktionary.org/wiki/kilo-)*** in Wiktionary, the free dictionary.

**Kilo** is a [unit prefix](/source/Unit_prefix) in the [metric system](/source/Metric_system) of measurement, denoting multiplication by one [thousand](/source/Thousand) (103). The [International System of Units](/source/International_System_of_Units) reserves the [lowercase](/source/Letter_case) symbol **k**.

*Kilo* is derived from the [Greek](/source/Greek_language) word χίλιοι (*chilioi*), meaning "thousand".

In 19th century English the prefix was sometimes spelled chilio, in line with a [puristic](/source/Linguistic_purism) opinion by [Thomas Young](/source/Thomas_Young_(scientist)).[1][2] As an opponent of suggestions to introduce the metric system in Britain, he qualified the nomenclature adopted in France as barbarous.

## Examples

- one [kilogram](/source/Kilogram) (kg) is 1000 [grams](/source/Gram)

- one [kilometre](/source/Kilometre) (km) is 1000 [metres](/source/Metre)

- one [kilojoule](/source/Kilojoule) (kJ) is 1000 [joules](/source/Joule)

- one kilolitre (kL) is 1000 [litres](/source/Litre)

- one kilobaud (kBd) is 1000 [bauds](/source/Baud)

- one kilohertz (kHz) is 1000 [hertz](/source/Hertz)

- one kilodalton (kDa) is 1000 [daltons](/source/Dalton_(unit))

- one [kilobit](/source/Kilobit) (kb) is 1000 [bits](/source/Bit)

- one [kilobyte](/source/Kilobyte) (kB) is 1000 [bytes](/source/Byte)

- one kiloohm is (kΩ) is 1000 [ohms](/source/Ohm)

- one [kilosecond](/source/Kilosecond) (ks) is 1000 [seconds](/source/Second)

- one [kilotonne](/source/Kilotonne) (kt) is 1000 [tonnes](/source/Tonne)

By extension, currencies are sometimes also preceded by the prefix:

- one kiloeuro (k€) is 1000 [euros](/source/Euro)

- one kilodollar (k$) is 1000 [dollars](/source/Dollar)

## kilobyte

For multiples of the [byte](/source/Byte) in some fields of [computer science](/source/Computer_science) and information technology, another definition has been in common use, in which the *kilobyte* measures 1024 bytes (210 bytes), because 210 is approximately 103. The reason for this application is that digital hardware natively use [base 2](/source/Base_2) exponentiation.

The [National Institute of Standards and Technology](/source/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."[3] A new set of [binary prefixes](/source/Binary_prefix), based on powers of 2, was introduced by the [International Electrotechnical Commission](/source/International_Electrotechnical_Commission) (IEC), which defines 1024 bytes as one [kibibyte](/source/Kibibyte) (1 KiB).

## Exponentiation

When units occur in [exponentiation](/source/Exponentiation), such as in square and cubic forms, any multiplier prefix is part of the unit, and thus included in the exponentiation.

- 1 km2 means one square kilometre or the area of a [square](/source/Square_(geometry)) that measures 1000 m on each side or 106 m2 (as opposed to 1000 square meters, which is the area of a square that measures 31.6 m on each side).

- 1 km3 means one cubic kilometre or the volume of a [cube](/source/Cube) that measures 1000 m on each side or 109 m3 (as opposed to 1000 cubic meters, which is the volume of a cube that measures 10 m on each side).

## See also

- [milli](/source/Milli-) (inverse of kilo, denoting a factor of 1/1000)

- [kibi](/source/Kibi-) (binary prefix, denoting a factor of 1024)

- [RKM code](/source/RKM_code)

## References

1. **[^](#cite_ref-Brewster_1832_1-0)** Brewster, David (1832). [*The Edinburgh Encyclopaedia*](https://books.google.com/books?id=17RGAQAAIAAJ&pg=PA572). Vol. 12 (1st American ed.). Joseph and Edward Parker. Retrieved 2015-10-09.

1. **[^](#cite_ref-Dingler_1823_2-0)** Dingler, Johann Gottfried (1823). [*Polytechnisches Journal*](https://books.google.com/books?id=wF3zAAAAMAAJ&pg=PA500) (in German). Vol. 11. Stuttgart, Germany: J.W. Gotta'schen Buchhandlung. Retrieved 2015-10-09.

1. **[^](#cite_ref-3)** [Definition of binary prefixes at NIST](http://physics.nist.gov/cuu/Units/binary.html)

SI prefixes v t e Prefix Base 10 Decimal Adoption [nb 1] Name Symbol quetta Q 1030 1000000000000000000000000000000 2022[1] ronna R 1027 1000000000000000000000000000 yotta Y 1024 1000000000000000000000000 1991 zetta Z 1021 1000000000000000000000 exa E 1018 1000000000000000000 1975[2] peta P 1015 1000000000000000 tera T 1012 1000000000000 1960 giga G 109 1000000000 mega M 106 1000000 1873 kilo k 103 1000 1795 hecto h 102 100 deca da 101 10 — — 100 1 — deci d 10−1 0.1 1795 centi c 10−2 0.01 milli m 10−3 0.001 micro μ 10−6 0.000001 1873 nano n 10−9 0.000000001 1960 pico p 10−12 0.000000000001 femto f 10−15 0.000000000000001 1964 atto a 10−18 0.000000000000000001 zepto z 10−21 0.000000000000000000001 1991 yocto y 10−24 0.000000000000000000000001 ronto r 10−27 0.000000000000000000000000001 2022[1] quecto q 10−30 0.000000000000000000000000000001 Notes ^ Prefixes adopted before 1960 already existed before SI. The introduction of the centimetre–gram–second system of units was in 1873.

1. ^ [***a***](#cite_ref-newUnitAdoption_5-0) [***b***](#cite_ref-newUnitAdoption_5-1) [*On the extension of the range of SI prefixes*](https://www.bipm.org/en/cgpm-2022/resolution-3). [CGPM](/source/General_Conference_on_Weights_and_Measures). *Resolution 3 of the 27th CGPM (2022)*. [BIPM](/source/International_Bureau_of_Weights_and_Measures). 18 November 2022. [doi](/source/Doi_(identifier)):[10.59161/cgpm2022res3e](https://doi.org/10.59161%2Fcgpm2022res3e). Retrieved 5 February 2023.

1. **[^](#cite_ref-6)** ["Metric (SI) Prefixes"](https://www.nist.gov/pml/owm/metric-si-prefixes). NIST.

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Adapted from the Wikipedia article [Kilo-](https://en.wikipedia.org/wiki/Kilo-) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Kilo-?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.