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Deca (International spelling as used by the International Bureau of Weights and Measures;[1] symbol: da) or deka (American spelling[2]) is a decimal unit prefix in the metric system denoting a factor of ten. The term is derived from the Greek déka (?) meaning ten.

The prefix was a part of the original metric system in 1795. It is not in very common usage, 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. Its use is more common in Central Europe. In German, Polish, Czech, Slovak, and Hungarian, deka (or deko) is common, and used in self-standing form, always meaning decagram. A runway number typically indicates its magnetic azimuth in decadegrees.

Before the symbol as an SI prefix was standardized as da with the introduction of the International System of Units in 1960, various other symbols were more common, such as dk (e.g., UK and Austria), D (e.g., Germany, Eastern Europe), and Da. For syntactical reasons, the HP 48, 49, 50 series, as well as the HP 39gII and Prime calculators use the unit prefix D.[3][4][5]


  • The blue whale is approximately 30 metres or 3 decametres in length.[6]
SI prefixes
Prefix Base 10 Decimal English word Adoption[nb 1] Etymology
Name Symbol Short scale Long scale Language Derived word
yotta Y  1024 1000000000000000000000000  septillion  quadrillion 1991 Greek eight[nb 2]
zetta Z  1021 1000000000000000000000  sextillion  trilliard 1991 Latin seven[nb 2]
exa E  1018 1000000000000000000  quintillion  trillion 1975 Greek six
peta P  1015 1000000000000000  quadrillion  billiard 1975 Greek five[nb 2]
tera T  1012 1000000000000  trillion  billion 1960 Greek four[nb 2], monster
giga G  109 1000000000  billion  milliard 1960 Greek giant
mega M  106 1000000  million 1873 Greek great
kilo k  103 1000  thousand 1795 Greek thousand
hecto h  102 100  hundred 1795 Greek hundred
deca da  101 10  ten 1795 Greek ten
 100 1  one -
deci d  10-1 0.1  tenth 1795 Latin ten
centi c  10-2 0.01  hundredth 1795 Latin hundred
milli m  10-3 0.001  thousandth 1795 Latin thousand
micro ?  10-6 0.000001  millionth 1873 Greek small
nano n  10-9 0.000000001  billionth  milliardth 1960 Greek dwarf
pico p  10-12 0.000000000001  trillionth  billionth 1960 Spanish peak
femto f  10-15 0.000000000000001  quadrillionth  billiardth 1964 Danish fifteen, Fermi[nb 3]
atto a  10-18 0.000000000000000001  quintillionth  trillionth 1964 Danish eighteen
zepto z  10-21 0.000000000000000000001  sextillionth  trilliardth 1991 Latin seven[nb 2]
yocto y  10-24  0.000000000000000000000001  septillionth  quadrillionth 1991 Greek eight[nb 2]
  1. ^ Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.
  2. ^ a b c d e f Part of the beginning of the prefix was modified from the word it was derived from, ex: "peta" (prefix) vs "penta" (derived word).
  3. ^ The fermi was introduced earlier with the same symbol "fm", in which then the "f" became a prefix. The Danish word is used since it is vaguely spelled similar to fermi.

See also


  1. ^ Decimal multiples and submultiples of SI units, 2006, SI Brochure: The International System of Units (SI), 8th edition
  2. ^ Guide for the Use of the International System of Units (SI), 1995, NIST Special Publication 811
  3. ^ HP 48G Series - User's Guide (UG) (8 ed.). Hewlett-Packard. December 1994 [1993]. HP 00048-90126, (00048-90104). Retrieved .
  4. ^ HP 50g graphing calculator user's guide (UG) (1 ed.). Hewlett-Packard. 2006-04-01. HP F2229AA-90006. Retrieved .
  5. ^ HP Prime Graphing Calculator User Guide (UG) (PDF) (1 ed.). Hewlett-Packard Development Company, L.P. October 2014. HP 788996-001. Archived from the original (PDF) on 2014-09-03. Retrieved .
  6. ^

External links

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