Kilo-
Decimal unit prefix in the metric system
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Through Metric system, 1000 (number) and International System of Units
Kilo is derived from the Greek word χίλιοι (chilioi), meaning "thousand".
In 19th century English the prefix was sometimes spelled chilio, in line with a puristic opinion by Thomas Young. 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:
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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 (210 bytes), because 210 is approximately 103. 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." 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 km2 means one square kilometre or the area of a square 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 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).