Kilo is a decimal unit prefix in the metric system denoting multiplication by one thousand (103). 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".

In 19th century English it was sometimes spelled chilio, in line with a puristic opinion by Thomas Young.[1][2] As an opponent of suggestions to introduce the metric system in Britain, he qualified the nomenclature adopted in France as barbarous.

ExamplesEdit

By extension, currencies are also sometimes preceded by the prefix kilo-:

  • one kiloeuro (k€) is 1000 euros
  • one kilodollar (k$) is 1000 dollars

kilobyteEdit

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 210 bytes (= 1024 bytes), because of the mathematical coincidence that 210 is approximately 103. 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).

ExponentiationEdit

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 alsoEdit

  • milli- (inverse of kilo- prefix, denoting a factor of 1/1000)
  • kibi- (binary prefix, denoting a factor of 1024)
  • RKM code

ReferencesEdit

  1. ^ Brewster, David (1832). The Edinburgh Encyclopaedia. 12 (1st American ed.). Joseph and Edward Parker. Retrieved 2015-10-09.
  2. ^ Dingler, Johann Gottfried (1823). Polytechnisches Journal (in German). 11. Stuttgart, Germany: J.W. Gotta'schen Buchhandlung. Retrieved 2015-10-09.
  3. ^ Definition of binary prefixes at NIST
SI prefixes
Prefix Base 10 Decimal English word Adoption[nb 1] Etymology
Name Symbol Short scale Long scale Language Derived word
yotta Y  1024 1000000000000000000000000  septillion  quadrillion 1991 Greek eight[nb 2]
zetta Z  1021 1000000000000000000000  sextillion  trilliard 1991 Latin seven[nb 2]
exa E  1018 1000000000000000000  quintillion  trillion 1975 Greek six
peta P  1015 1000000000000000  quadrillion  billiard 1975 Greek five[nb 2]
tera T  1012 1000000000000  trillion  billion 1960 Greek four[nb 2], monster
giga G  109 1000000000  billion  milliard 1960 Greek giant
mega M  106 1000000  million 1873 Greek great
kilo k  103 1000  thousand 1795 Greek thousand
hecto h  102 100  hundred 1795 Greek hundred
deca da  101 10  ten 1795 Greek ten
 100 1  one
deci d  10−1 0.1  tenth 1795 Latin ten
centi c  10−2 0.01  hundredth 1795 Latin hundred
milli m  10−3 0.001  thousandth 1795 Latin thousand
micro μ  10−6 0.000001  millionth 1873 Greek small
nano n  10−9 0.000000001  billionth  milliardth 1960 Greek dwarf
pico p  10−12 0.000000000001  trillionth  billionth 1960 Spanish peak
femto f  10−15 0.000000000000001  quadrillionth  billiardth 1964 Danish fifteen, Fermi[nb 3]
atto a  10−18 0.000000000000000001  quintillionth  trillionth 1964 Danish eighteen
zepto z  10−21 0.000000000000000000001  sextillionth  trilliardth 1991 Latin seven[nb 2]
yocto y  10−24  0.000000000000000000000001  septillionth  quadrillionth 1991 Greek eight[nb 2]
  1. ^ Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.
  2. ^ a b c d e f Part of the beginning of the prefix was modified from the word it was derived from, ex: "peta" (prefix) vs "penta" (derived word).
  3. ^ The fermi was introduced earlier with the same symbol "fm", in which then the "f" became a prefix. The Danish word is used since it is vaguely spelled similar to fermi.