Kilo-

For other uses, see Kilo (disambiguation).

kilo is a unit prefix in the metric system denoting multiplication by one thousand. It has been used in the International System of Units where it has the unit 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.

Examples:

• one kilogram is 1000 grams
• one kilometre is 1000 metres
• one kilojoule is 1000 joules
• one kilobaud is 1000 bauds
• one kilobit is 1000 bits
• one kilobyte is 1000 bytes.

A second definition has been in common use in some fields of computer science and information technology, which is, however, inconsistent with the SI. It uses kilo as meaning 2¹⁰ = 1024, because of the mathematical coincidence that 2¹⁰ is approximately 10³. The NIST comments on this confusion: "Faced with this reality, the IEEE Standards Board decided that IEEE standards will use the conventional, internationally adopted, definitions of the SI prefixes."

• one kilohertz is 1000 hertz

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 of 1000 m by 1000 m or 10⁶ m².
• 1 km³ means one cubic kilometre or the volume of a cube of 1000 m by 1000 m by 1000 m or 10⁹ m³.

See also

• International System of Units

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