Kilo-

For other uses, seeKilo (disambiguation).

Kilois adecimalunit prefixin themetric systemdenoting multiplication by onethousand(10³). It is used in theInternational System of Units,where it has the symbolk,inlowercase.

The prefixkilois derived from theGreekwordχίλιοι(chilioi), meaning "thousand".

In 19th century English it was sometimes spelled chilio, in line with apuristicopinion byThomas Young.As an opponent of suggestions to introduce the metric system in Britain, he qualified the nomenclature adopted in France as barbarous.

Examples

• onekilogram(kg) is 1000grams
• onekilometre(km) is 1000metres
• onekilojoule(kJ) is 1000joules
• one kilolitre (kL) is 1000litres
• one kilobaud (kBd) is 1000bauds
• one kilohertz (kHz) is 1000hertz
• one kilodalton (kDa) is 1000daltons
• onekilobit(kb) is 1000bits
• onekilobyte(kB) is 1000bytes
• one kiloohm is (kΩ) is 1000ohms
• onekilosecond(ks) is 1000seconds
• onekilotonne(kt) is 1000tonnes

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

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

kilobyte

For the kilobyte, a second definition has been in common use in some fields ofcomputer scienceand information technology. It useskilobyteto mean 2¹⁰bytes (= 1024 bytes), because of themathematical coincidencethat 2¹⁰is approximately 10³.The reason for this application is that digital hardware and architectures natively usebase 2exponentiation, and notdecimalsystems.JEDEC memory standardsstill permit this definition, but acknowledge the correct SI usage.

NIST comments on the confusion caused by these contrasting definitions: "Faced with this reality, theIEEE Standards Boarddecided that IEEE standards will use the conventional, internationally adopted, definitions of the SI prefixes ", instead of kilo for 1024.To address this conflict, a new set ofbinary prefixeshas been introduced, which is based on powers of 2. Therefore, 1024 bytes are defined as onekibibyte(1 KiB).

Exponentiation

When units occur inexponentiation,such as in square and cubic forms, any multiplier prefix is considered part of the unit, and thus included in the exponentiation.

• 1 km²means one square kilometre or the area of asquarethat measures 1000 m on each side or 10⁶m²(as opposed to 1000 square meters, which is the area of a square that measures 31.6 m on each side).
• 1 km³means one cubic kilometre or the volume of acubethat measures 1000 m on each side or 10⁹m³(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

SI prefixes

Prefix		Base 10	Decimal	Adoption
Name	Symbol
quetta	Q	1030	1000000000000000000000000000000	2022
ronna	R	1027	1000000000000000000000000000
yotta	Y	1024	1000000000000000000000000	1991
zetta	Z	1021	1000000000000000000000
exa	E	1018	1000000000000000000	1975
peta	P	1015	1000000000000000
tera	T	1012	1000000000000	1960
giga	G	109	1000000000
mega	M	106	1000000	1873
kilo	k	103	1000	1795
hecto	h	102	100
deca	da	101	10
—	—	100	1	—
deci	d	10−1	0.1	1795
centi	c	10−2	0.01
milli	m	10−3	0.001
micro	μ	10−6	0.000001	1873
nano	n	10−9	0.000000001	1960
pico	p	10−12	0.000000000001
femto	f	10−15	0.000000000000001	1964
atto	a	10−18	0.000000000000000001
zepto	z	10−21	0.000000000000000000001	1991
yocto	y	10−24	0.000000000000000000000001
ronto	r	10−27	0.000000000000000000000000001	2022
quecto	q	10−30	0.000000000000000000000000000001
Notes