Kilo-

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.

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-:

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

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 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).

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 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).

References

Brewster, David (1832). The Edinburgh Encyclopaedia. Vol. 12 (1st American ed.). Joseph and Edward Parker. Retrieved 2015-10-09.
Dingler, Johann Gottfried (1823). Polytechnisches Journal (in German). Vol. 11. Stuttgart, Germany: J.W. Gotta'schen Buchhandlung. Retrieved 2015-10-09.
Definition of binary prefixes at NIST

SI prefixes
Prefix		Base 10	Decimal	English word		Adoption[nb 1]	Etymology
Name	Symbol	Base 10	Decimal	Short scale	Long scale	Adoption[nb 1]	Language	Source word
yotta	Y	10²⁴	1000000000000000000000000	septillion	quadrillion	1991	Latin	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, a little bit
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	Latin	eight[nb 2]
Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873. Part of the beginning of the prefix was modified from the word it was derived from, ex: "peta" (prefix) vs "penta" (source word). The fermi was introduced earlier with the symbol "fm", which prompted the reinterpretation of the "f" as a prefix to "m", with femto being derived from the Danish word femten due to its similarity.

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[Brewster_1832-1] Brewster, David (1832). The Edinburgh Encyclopaedia. Vol. 12 (1st American ed.). Joseph and Edward Parker. Retrieved 2015-10-09.

[Dingler_1823-2] Dingler, Johann Gottfried (1823). Polytechnisches Journal (in German). Vol. 11. Stuttgart, Germany: J.W. Gotta'schen Buchhandlung. Retrieved 2015-10-09.

[3] Definition of binary prefixes at NIST

[4] Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.

[similar-5] Part of the beginning of the prefix was modified from the word it was derived from, ex: "peta" (prefix) vs "penta" (source word).

[6] The fermi was introduced earlier with the symbol "fm", which prompted the reinterpretation of the "f" as a prefix to "m", with femto being derived from the Danish word femten due to its similarity.

Kilo-

Examples

kilobyte

Exponentiation

See also

References