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:
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 JEDECstandard, 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).
See also
References

^ Definition of binary prefixes at NIST

Prefix

1000^{m}

10^{n}

Decimal

English word

Since^{[n 1]}

name

symbol

short scale

long scale

yotta

Y

1000^{8}

10^{24}

1000000000000000000000000

septillion

quadrillion

1991

zetta

Z

1000^{7}

10^{21}

1000000000000000000000

sextillion

thousand trillion

1991

exa

E

1000^{6}

10^{18}

1000000000000000000

quintillion

trillion

1975

peta

P

1000^{5}

10^{15}

1000000000000000

quadrillion

thousand billion

1975

tera

T

1000^{4}

10^{12}

1000000000000

trillion

billion

1960

giga

G

1000^{3}

10^{9}

1000000000

billion

thousand million

1960

mega

M

1000^{2}

10^{6}

1000000

million

1960

kilo

k

1000^{1}

10^{3}

1000

thousand

1795

hecto

h

1000^{2/3}

10^{2}

100

hundred

1795

deca

da

1000^{1/3}

10^{1}

10

ten

1795


1000^{0}

10^{0}

1

one

–

deci

d

1000^{−1/3}

10^{−1}

0.1

tenth

1795

centi

c

1000^{−2/3}

10^{−2}

0.01

hundredth

1795

milli

m

1000^{−1}

10^{−3}

0.001

thousandth

1795

micro

μ

1000^{−2}

10^{−6}

0.000001

millionth

1960

nano

n

1000^{−3}

10^{−9}

0.000000001

billionth

thousand millionth

1960

pico

p

1000^{−4}

10^{−12}

0.000000000001

trillionth

billionth

1960

femto

f

1000^{−5}

10^{−15}

0.000000000000001

quadrillionth

thousand billionth

1964

atto

a

1000^{−6}

10^{−18}

0.000000000000000001

quintillionth

trillionth

1964

zepto

z

1000^{−7}

10^{−21}

0.000000000000000000001

sextillionth

thousand trillionth

1991

yocto

y

1000^{−8}

10^{−24}

0.000000000000000000000001

septillionth

quadrillionth

1991




^ The metric system was introduced in 1795 with six prefixes. The other dates relate to recognition by a resolution of the CGPM.
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