# Kilo-

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**kilo** is a unit prefix in the metric system denoting multiplication by one thousand. It has been used in the International System of Units where it has the unit symbol **k**, in lower case.

The prefix *kilo* is derived from the Greek word χίλιοι (*chilioi*), meaning "thousand". It was originally adopted by Antoine Lavoisier's research group in 1795, and introduced into the metric system in France with its establishment in 1799.

Examples:

- one kilogram is 1000 grams
- one kilometre is 1000 metres
- one kilojoule is 1000 joules
- one kilobaud is 1000 bauds
- one kilohertz is 1000 hertz
- one kilobit is 1000 bits
- one kilobyte (
*kB*) is 1000 bytes (see exception below for*KB*)

A second definition has been in common use in some fields of computer science and information technology, which is, however, inconsistent with the SI. It uses kilo as meaning 2^{10} = 1024, because of the mathematical coincidence that 2^{10} is approximately 10^{3}. The NIST comments on this confusion: "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.^{[1]}

Example:

- One "Kilobyte" (
*KB*) is 1024 bytes in JEDEC-standard, whereas the definition has shifted to, in most contexts, mean 1000 bytes (*kB*) in accordance with SI.

## 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 km
^{2}means one square kilometre or the area of a square that measures 1000 m on each side or 10^{6}m^{2}(as opposed to 1000 square meters, which is the area of a square that measures 31.6 m on each side). - 1 km
^{3}means one cubic kilometre or the volume of a cube that measures 1000 m on each side or 10^{9}m^{3}(as opposed to 1000 cubic meters, which is the volume of a cube that measures 10 m on each side).