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Title: Kilo-  
Author: World Heritage Encyclopedia
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Subject: Binary prefix, Metric prefix, Byte, History of radiation therapy, Y2K (disambiguation)
Collection: Metric Prefixes, Si Prefixes
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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.


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 210 = 1024, because of the mathematical coincidence that 210 is approximately 103. 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]


  • 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.


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 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).

See also


  1. ^ Definition of binary prefixes at NIST
Prefix 1000m 10n Decimal English word Since[n 1]
name symbol short scale long scale
yotta Y  10008  1024 1000000000000000000000000  septillion  quadrillion 1991
zetta Z  10007  1021 1000000000000000000000  sextillion  thousand trillion 1991
exa E  10006  1018 1000000000000000000  quintillion  trillion 1975
peta P  10005  1015 1000000000000000  quadrillion  thousand billion 1975
tera T  10004  1012 1000000000000  trillion  billion 1960
giga G  10003  109 1000000000  billion  thousand million 1960
mega M  10002  106 1000000             million 1960
kilo k  10001  103 1000             thousand 1795
hecto h  10002/3  102 100             hundred 1795
deca da  10001/3  101 10             ten 1795
 10000  100 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
  1. ^ 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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