Peta-

This article describes the SI prefix. For other meanings, see Peta.

Peta- (symbol: P) is a prefix in the metric system denoting 10¹⁵ or 1000000000000000. For example:

1 petametre = 10¹⁵ metres
1 petasecond = 10¹⁵ seconds
1 petabyte = 10¹⁵ bytes

Adopted in 1975, it was derived from the Greek πέντε, meaning "five", because of the five in 1000⁵, for which it stands. The peta- prefix is similar to the penta- prefix (for "five"), but without the letter n. This omission is modelled on the way the similar tera- prefix (actually from Greek τέρας = 'monster') for 1000⁴ seems to omit a letter from the tetra- prefix (for "four").

Examples:

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

In computer science peta- can sometimes mean 1125899906842624 (1024⁵ or 2⁵⁰), instead of 1000000000000000, especially when used to prefix the byte, giving a petabyte. To resolve this ambiguity, the term pebibyte has been suggested to mean 2⁵⁰ bytes.

SI prefixes

Prefix	Symbol	1000m	10n	Decimal	Short scale	Long scale	Since
yotta	Y	10008	1024	1000000000000000000000000	Septillion	Quadrillion	1991
zetta	Z	10007	1021	1000000000000000000000	Sextillion	Trilliard	1991
exa	E	10006	1018	1000000000000000000	Quintillion	Trillion	1975
peta	P	10005	1015	1000000000000000	Quadrillion	Billiard	1975
tera	T	10004	1012	1000000000000	Trillion	Billion	1960
giga	G	10003	109	1000000000	Billion	Milliard	1960
mega	M	10002	106	1000000	Million		1960
kilo	k	10001	103	1000	Thousand		1795
hecto	h	10002/3	102	100	Hundred		1795
deca	da	10001/3	101	10	Ten		1795
		10000	100	1	One		–
deci	d	1000−1/3	10−1	0.1	Tenth		1795
centi	c	1000−2/3	10−2	0.01	Hundredth		1795
milli	m	1000−1	10−3	0.001	Thousandth		1795
micro	μ	1000−2	10−6	0.000001	Millionth		1960
nano	n	1000−3	10−9	0.000000001	Billionth	Milliardth	1960
pico	p	1000−4	10−12	0.000000000001	Trillionth	Billionth	1960
femto	f	1000−5	10−15	0.000000000000001	Quadrillionth	Billiardth	1964
atto	a	1000−6	10−18	0.000000000000000001	Quintillionth	Trillionth	1964
zepto	z	1000−7	10−21	0.000000000000000000001	Sextillionth	Trilliardth	1991
yocto	y	1000−8	10−24	0.000000000000000000000001	Septillionth	Quadrillionth	1991

See also

• Binary prefix

External links

• BIPM website