Look up kilo in Wiktionary, the free dictionary. 
Kilo is a decimal unit prefix in the metric system denoting multiplication by one thousand (10^{3}). It is used in the International System of Units, where it has the 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.
In 19th century English it was sometimes spelled chilio, in line with a puristic opinion by Thomas Young.^{[1]}^{[2]}
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 baud
 one kilohertz (kHz) is 1000 hertz
 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 also sometimes preceded by the prefix kilo:
kilobyte
For the kilobyte, a second definition has been in common use in some fields of computer science and information technology. It uses kilobyte to mean 2^{10} bytes (= 1024 bytes), because of the mathematical coincidence that 2^{10} is approximately 10^{3}. The reason for this application is that digital hardware and architectures natively use base 2 exponentiation, and not decimal systems. JEDEC memory standards still permit this definition, but acknowledge the correct SI usage.
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", instead of kilo for 1024.^{[3]} To address this conflict, a new set of binary prefixes has been introduced, which is based on powers of 2. Therefore, 1024 bytes are defined as one kibibyte (1 KiB).
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
 milli (inverse of kilo prefix, denoting a factor of 1/1000)
 kibi (binary prefix, denoting a factor of 1024)
 RKM code
References
 ^ Brewster, David (1832). The Edinburgh Encyclopaedia. 12 (1st American ed.). Joseph and Edward Parker. Retrieved 20151009.
 ^ Dingler, Johann Gottfried (1823). Polytechnisches Journal (in German). 11. Stuttgart, Germany: J.W. Gotta'schen Buchhandlung. Retrieved 20151009.
 ^ Definition of binary prefixes at NIST
Prefix  Base 10  Decimal  English word  Adoption^{[nb 1]}  

Name  Symbol  Short scale  Long scale  
yotta  Y  10^{24}  1000000000000000000000000  septillion  quadrillion  1991  
zetta  Z  10^{21}  1000000000000000000000  sextillion  trilliard  1991  
exa  E  10^{18}  1000000000000000000  quintillion  trillion  1975  
peta  P  10^{15}  1000000000000000  quadrillion  billiard  1975  
tera  T  10^{12}  1000000000000  trillion  billion  1960  
giga  G  10^{9}  1000000000  billion  milliard  1960  
mega  M  10^{6}  1000000  million  1873  
kilo  k  10^{3}  1000  thousand  1795  
hecto  h  10^{2}  100  hundred  1795  
deca  da  10^{1}  10  ten  1795  
10^{0}  1  one  –  
deci  d  10^{−1}  0.1  tenth  1795  
centi  c  10^{−2}  0.01  hundredth  1795  
milli  m  10^{−3}  0.001  thousandth  1795  
micro  μ  10^{−6}  0.000001  millionth  1873  
nano  n  10^{−9}  0.000000001  billionth  milliardth  1960  
pico  p  10^{−12}  0.000000000001  trillionth  billionth  1960  
femto  f  10^{−15}  0.000000000000001  quadrillionth  billiardth  1964  
atto  a  10^{−18}  0.000000000000000001  quintillionth  trillionth  1964  
zepto  z  10^{−21}  0.000000000000000000001  sextillionth  trilliardth  1991  
yocto  y  10^{−24}  0.000000000000000000000001  septillionth  quadrillionth  1991  
