Kilo-

For other uses, see Kilo (disambiguation).

Look up kilo- in Wiktionary, the free dictionary.

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". 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-:

• 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).

See also

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

References

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

• v
• t
• e

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[nb 3]	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[nb 3]	10−12	0.000000000001	trillionth	billionth	1960	Spanish	small
femto	f	10−15	0.000000000000001	quadrillionth	billiardth	1964	Danish	fifteen
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]
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" (derived word). Uppercase P and lowercase p do not indicate the same power of ten for their respective multiples, rather powers of 15 and 12 respectively.