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Deca- or deka- (symbol da) is a decimal unit prefix in the metric system, denoting a factor of ten. The term is derived from the Greek , meaning "ten".

The prefix was a part of the original metric system in 1795. It is not in very common usage, although the deca pascal is occasionally used by audiologists. The deca newton 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 (deka, deko), Czech, Slovak and Hungarian, deca is common (and used a word on its own always means decagram). A runway number typically indicates its heading 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" (f.e. in the UK and Austria), "D" (f.e. in Germany), 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".


  • The blue whale is approximately 30 meters or 3 decameters in length.

Deca- (prefix)

Deca- (and dec-) sometimes deka- is a common English-language prefix derived from the Late Latin ("(set of) ten"), from Ancient Greek , from (déka, " ten"). It is used in many words.

The Collaborative International Dictionary


Deca- \Dec"a-\ pref. [Cf. Ten.] A prefix, from Gr. de`ka, signifying ten; specifically (Metric System), a prefix signifying the weight or measure that is ten times the principal unit. [1913 Webster] ||

Douglas Harper's Etymology Dictionary


before a vowel, dec-, word-forming element meaning "ten," from Latinized comb. form of Greek deka "ten" (see ten). In the metric system, "multiplied by ten;" while deci- means "divided by ten."



pre. 1 ten. 2 In the International System of Units and other metric systems of units, multiplying the unit to which it is attached by 10. Symbol: da

Longman Dictionary of Contemporary English


▪ decaliter