Peta-

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This article describes the SI prefix. For other meanings, including People for the Ethical Treatment of Animals, see Peta.

In physics and mathematics, peta- (symbol: P) is a prefix in the SI (system of units) denoting 10¹⁵, or 1 000 000 000 000 000. For example: 1 petametre = 10¹⁵ metres 1 petasecond = 10¹⁵ seconds Adopted in 1975, it comes from the Greek πέντε, meaning five, because it is equal to 1000⁵. It is based on the model of tera- (from Greek τέρας = 'monster', but looking like tetra- from the Greek for "four" with a letter missing), and so peta-, coming from penta-, omits the third letter, n. Examples:

the mass–energy equivalence is 89.9 PJ/kg
1 light-year = 9.461 Pm

In computer science peta- can sometimes mean 1 125 899 906 842 624 (1024⁵ or 2⁵⁰), instead of 1 000 000 000 000 000, especially when used to prefix the byte, giving a petabyte. To resolve this ambiguity, the term pebibyte has been suggested to mean 2⁵⁰ bytes. However, this term is not yet widely used.

SI prefixes
1000ⁿ	10ⁿ	Prefix	Symbol	Since^[1]	Short scale	Long scale	Decimal equivalent in SI writing style
1000⁸	10²⁴	yotta-	Y	1991	Septillion	Quadrillion	1 000 000 000 000 000 000 000 000
1000⁷	10²¹	zetta-	Z	1991	Sextillion	Trilliard (thousand trillion)	1 000 000 000 000 000 000 000
1000⁶	10¹⁸	exa-	E	1975	Quintillion	Trillion	1 000 000 000 000 000 000
1000⁵	10¹⁵	peta-	P	1975	Quadrillion	Billiard (thousand billion)	1 000 000 000 000 000
1000⁴	10¹²	tera-	T	1960	Trillion	Billion	1 000 000 000 000
1000³	10⁹	giga-	G	1960	Billion	Milliard (thousand million)	1 000 000 000
1000²	10⁶	mega-	M	1960	Million		1 000 000
1000¹	10³	kilo-	k	1795	Thousand		1 000
1000^2/3	10²	hecto-	h	1795	Hundred		100
1000^1/3	10¹	deca-	da	1795	Ten		10
1000⁰	10⁰	(none)	(none)	NA	One		1
1000^−1/3	10⁻¹	deci-	d	1795	Tenth		0.1
1000^−2/3	10⁻²	centi-	c	1795	Hundredth		0.01
1000⁻¹	10⁻³	milli-	m	1795	Thousandth		0.001
1000⁻²	10⁻⁶	micro-	µ	1960^[2]	Millionth		0.000 001
1000⁻³	10⁻⁹	nano-	n	1960	Billionth	Milliardth	0.000 000 001
1000⁻⁴	10⁻¹²	pico-	p	1960	Trillionth	Billionth	0.000 000 000 001
1000⁻⁵	10⁻¹⁵	femto-	f	1964	Quadrillionth	Billiardth	0.000 000 000 000 001
1000⁻⁶	10⁻¹⁸	atto-	a	1964	Quintillionth	Trillionth	0.000 000 000 000 000 001
1000⁻⁷	10⁻²¹	zepto-	z	1991	Sextillionth	Trilliardth	0.000 000 000 000 000 000 001
1000⁻⁸	10⁻²⁴	yocto-	y	1991	Septillionth	Quadrillionth	0.000 000 000 000 000 000 000 001
Notes: 1. The 1795 dates identify prefixes in use since the metric system was introduced. The other dates are not necessarily dates of first use, but rather the date of recognition by a resolution of the CGPM, which first met in 1889. 2. The micron was earlier recognized by the CGPM in 1948; that decision was abrogated in 1967-68.