International System Prefixes

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The SI prefixes are used to name multiples and submultiples of any SI unit, whether they are base or derived units. These prefixes are placed before the name of the unit to indicate the decimal multiple or submultiple of it; similarly, prefix symbols precede unit symbols.

The SI prefixes are officially set by the International Bureau of Weights and Measures (Bureau International des Poids et Mesures), according to the following table:

1000ⁿ	10ⁿ	Prefix	Symbol	Short scale	Long scale	Decimal equity in the prefixes of the International System	Allocation
1000¹⁰	10³⁰	quetta-	Q	Nonillion	Quintillón	1 000 000 000 000 000 000 000 000	2022
1000⁹	10²⁷	ronna-	R	Eighth	Mil cuatrillones	1 000 000 000 000 000 000 000 000	2022
1000⁸	10²⁴	Yotta-	And	Septillion	Cuatrillón	1 000 000 000 000 000 000 000	1991
1000⁷	10²¹	zetta-	Z	Sextillion	A thousand trillions	1 000 000 000 000 000 000	1991
1000⁶	10¹⁸	exa...	E	Quintillón	Trillion	1 000 000 000 000 000 000	1975
1000⁵	10¹⁵	peta...	P	Cuatrillón	A billion.	1 000 000 000 000 000	1975
1000⁴	10¹²	tera-	T	Trillion	Billion	1 000 000 000 000	1960
1000³	10⁹	giga-	G	Billion	billion / billion	1 000 000 000	1960
1000²	10⁶	mega-	M	Million		1 000	1960
1000¹	10³	kilo-	k	Mil / Millar		1 000	1795
1000^2/3	10²	Hecto-	h	Hundred / Hundred		100	1795
1000^1/3	10¹	deca-	da	Ten / Ten		10	1795
1000⁰	10⁰	No prefix		One / Unit		1
1000^−1/3	10⁻¹	deci-	d	Tenth		0.1	1795
1000^−2/3	10⁻²	centi-	c	Centésimo		0.01	1795
1000⁻¹	10⁻³	mili-	m	A thousandth		0.001	1795
1000⁻²	10⁻⁶	micro-	μ	Millions		0.000 001	1960
1000⁻³	10⁻⁹	nano-	n	Billionth	One billion dollars	0.000 000 001	1960
1000⁻⁴	10⁻¹²	peak...	p	Trillonéimo	Billionth	0.000 000 000 001	1960
1000⁻⁵	10⁻¹⁵	femto-	f	Cuatrillonésimo	Milbillonésimo	0.000 000 000 000 001	1964
1000⁻⁶	10⁻¹⁸	Atto-	a	Quintillonésimo	Trillonéimo	0.000 000 000 000 000 000 001	1964
1000⁻⁷	10⁻²¹	zepto-	z	Sextillonésimo	Miltrillonésimo	0.000 000 000 000 000 000 000 001	1991
1000⁻⁸	10⁻²⁴	Icto-	and	Septillonésimo	Cuatrillonésimo	0.000 000 000 000 000 000 000 000 000 001	1991
1000⁻⁹	10⁻²⁷	red.	r	Eighth.	Milcuatrillonésimo	0.000 000 000 000 000 000 000 000 000 000 001	2022
1000⁻¹⁰	10⁻³⁰	Quecto-	q	Nonillonésimo	Quintillonésimo	0.000 000 000 000 000 000 000 000 000 000 000 001	2022

Notes on its use

You can't put two or more prefixes together: for example, 10⁻⁹ meters you have to write them as 1 nm, not 1 mμm.

Employment outside the IS

The symbol "K" (capitalized) is often used to mean a multiple of a thousand; therefore, it can be written "salary of 40K" (of 40,000 euros) or "the problem of the year 2K".^{[citation needed]} Despite the usual use, this use of the capital K is not correct in the SI, since it is the symbol for Kelvin units of temperature. The use of the abbreviation Ki is used to represent the binary prefix kibi (2¹⁰ = 1024).

Proposed extensions

Continuing backwards in the alphabet, after zetta and yotta, among the proposals to name the next large numbers are the words xenta and xona (among others), the latter being a modification of the numerical suffix from Latin nona-; the proposal for the following small numbers would also begin with "x".

Summary of employment rules

In accordance with the general principles adopted by (ISO 31), the International Committee on Weights and Measures (CIPM) recommends that the following rules be observed when using the above prefixes:

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