Hecto-

Hecto (symbol: h) is a decimal unit prefix in the metric system denoting a factor of one hundred. It was adopted as a multiplier in 1795, and comes from the Greek ἑκατόν hekatón, meaning "hundred". In 19th century English it was sometimes spelled "hecato", in line with a puristic opinion by Thomas Young.^[1][2] Its unit symbol as an SI prefix in the International System of Units (SI) is the lower case letter h.

The prefix is rarely used in general, but has certain specific applications:

• hectopascal (hPa), in meteorology, for atmospheric pressure, the modern equivalent of the traditional millibar.
• hectolitre (hl or hL), in agriculture, for liquids (notably milk and alcoholic beverages) and bulk commodities (e.g., grain).
• hectogram (hg), in agronomy, for quantities of animal feed (hectogram/animal) and for measures of agricultural productivity (hectogram/hectare); also used in Italy abbreviated as etto, and in Canada, New Zealand and Sweden simply as 100 g, for retail sale of cold cuts and meat.
• hectometre (hm), in radio astronomy, occasionally used to indicate a radio band by wavelength
• In surveying, a square hectometre is called a hectare (ha, or 100 ares = 1 hm² = 10,000 m²).

SI prefixes

• v
• t
• e

Prefix		Base 10	Decimal	Adoption [nb 1]
Name	Symbol
quetta	Q	1030	1000000000000000000000000000000	2022[3]
ronna	R	1027	1000000000000000000000000000
yotta	Y	1024	1000000000000000000000000	1991
zetta	Z	1021	1000000000000000000000
exa	E	1018	1000000000000000000	1975[4]
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[3]
quecto	q	10−30	0.000000000000000000000000000001
Notes Prefixes adopted before 1960 already existed before SI. The introduction of the centimetre–gram–second system of units was in 1873.

See also

• Metric prefix
• Numeral prefix