Deca- (and dec-), sometimes deka-, is a common English-language numeral prefix derived from the Late Latin decas ("(set of) ten"), from Ancient Greek δέκας (dékas), from δέκα (déka, "ten").[1] It is used in many words.

It is also a decimal unit prefix in the International System of Units (SI) denoting a factor of ten, with symbol da and spelled "deca" internationally[a] (or "deka" in American spelling[3]).

## SI

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.[4][5][6]

Examples:

• The blue whale is approximately 30 metres or 3 decametres in length.[7]
[nb 1]
Name Symbol
quetta Q 1030 1000000000000000000000000000000 2022[8]
ronna R 1027 1000000000000000000000000000
yotta Y 1024 1000000000000000000000000 1991
zetta Z 1021 1000000000000000000000
exa E 1018 1000000000000000000 1975[9]
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[8]
quecto q 10−30 0.000000000000000000000000000001
Notes
1. ^ Prefixes adopted before 1960 already existed before SI. The introduction of the CGS system was in 1873.

## As an English prefix

The prefix is used in many words.

### General

• Decathlon, a combined event in athletics consisting of ten track and field events.
• Decennial, ten-yearly or a celebration of ten years.

### Chemistry

• Decane, a hydrocarbon with 10 carbon atoms

### Biology

• Decapoda, an order of crustaceans with ten feet

## References

1. ^ Chambers Twentieth Century Dictionary. 1979. p. 332.
2. ^ Decimal multiples and submultiples of SI units Archived 2019-03-30 at the Wayback Machine, 2006, SI Brochure: The International System of Units (SI), 8th edition
3. ^ Guide for the Use of the International System of Units (SI), 1995, NIST Special Publication 811
4. ^ HP 48G Series – User's Guide (UG) (8 ed.). Hewlett-Packard. December 1994 [1993]. HP 00048-90126, (00048-90104). Retrieved 2015-09-06.
5. ^ HP 50g graphing calculator user's guide (UG) (1 ed.). Hewlett-Packard. 2006-04-01. HP F2229AA-90006. Retrieved 2015-10-10.
6. ^ 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 2015-10-13.
7. ^ "National Geographic TV Shows, Specials & Documentaries". Archived from the original on March 6, 2009.
8. ^ a b "On the extension of the range of SI prefixes". 18 November 2022. Retrieved 5 February 2023.
9. ^ "Metric (SI) Prefixes". NIST.