deca-

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This article is about the SI prefix. For other uses, see Deca.

Look up deca- in Wiktionary, the free dictionary.

deca or deka^[1] is an SI prefix (symbol da) in the SI system of units, also a numerical prefix (from Greek δέκα), denoting a factor of 10¹ or ten.

The prefix was a part of the original metric system in 1795. It is not in very common usage in English-speaking countries, although the decapascal is occasionally used by audiologists. The decanewton is also encountered occasionally, probably because it is an SI approximation of the kilogram-force. It is more commonly used in other languages: in Austrian and Hungarian, deca is common (and always means decagram).

Before the symbol was standardized as da with the introduction of the SI in 1960, various other symbols were more common, such as "dk", "D", and "Da".

1 decametre = 10 metres
1 decalitre = 10 litres
1 decare = 10 ares

SI prefixes
1000^m	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
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		0.000001
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.