hecto-

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hecto or hecta (symbol h) is a SI prefix in the SI system of units denoting a factor of 10² (100).

Adopted in 1795, it comes from the Greek ἑκατόν hekaton, meaning hundred.

It is rarely used, except for certain specific applications:

• hectopascal, in meteorology, for atmospheric pressure, the modern equivalent of the traditional millibar.
• hectolitre, in agriculture, for liquids (notably wine and milk) and bulk commodities (e.g. grain).
• hectogram, in agronomy, for quantities of animal feed (hectogram/animal) and for measures of agricultural productivity (hectogram/hectare); also used in Italy, abbreviated as etto, for retail sale of cold cuts and meat.
• hectometre, in radio astronomy, occasionally used to indicate a radio band by wavelength, an area of 1 hectometre² is also known as hectare.

SI prefixes

1000m	10n	Prefix	Symbol	Since[1]	Short scale	Long scale	Decimal
10008	1024	yotta	Y	1991	Septillion	Quadrillion	1000000000000000000000000
10007	1021	zetta	Z	1991	Sextillion	Trilliard	1000000000000000000000
10006	1018	exa	E	1975	Quintillion	Trillion	1000000000000000000
10005	1015	peta	P	1975	Quadrillion	Billiard	1000000000000000
10004	1012	tera	T	1960	Trillion	Billion	1000000000000
10003	109	giga	G	1960	Billion	Milliard	1000000000
10002	106	mega	M	1960	Million		1 000 000
10001	103	kilo	k	1795	Thousand		1000
10002⁄3	102	hecto	h	1795	Hundred		100
10001⁄3	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		0.000001
1000−3	10−9	nano	n	1960	Billionth	Milliardth	0.000000001
1000−4	10−12	pico	p	1960	Trillionth	Billionth	0.000000000001
1000−5	10−15	femto	f	1964	Quadrillionth	Billiardth	0.000000000000001
1000−6	10−18	atto	a	1964	Quintillionth	Trillionth	0.000000000000000001
1000−7	10−21	zepto	z	1991	Sextillionth	Trilliardth	0.000000000000000000001
1000−8	10−24	yocto	y	1991	Septillionth	Quadrillionth	0.000000000000000000000001
The metric system was introduced in 1795 with six prefixes. The other dates relate to recognition by a resolution of the CGPM. The 1948 recognition of the micron by the CGPM was abrogated in 1967.

[edit] See also

• SI prefix
• Numerical prefix