# Deca-

Deca (and dec), sometimes deka, is a common English-language numeral prefix derived from the Late Latin decas ("(set of) ten"), from Ancient Greek δεκάς (dekás), from δέκα (déka, "ten"). 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 (or "deka" in American spelling).

## 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.
* 1 decametre = 10 metres
* 1 decalitre = 10 litres
* 1 decare = 10 ares
Examples:
* The blue whale is approximately 30 metres or 3 decametres in length.
SI prefixesvte :
| Prefix | Prefix | Base 10 | Decimal | Adoption |
| Name | Symbol | Base 10 | Decimal | Adoption |
| quetta | Q | 10$^{30}$ | 1000000000000000000000000000000 | 2022 |
| ronna | R | 10$^{27}$ | 1000000000000000000000000000 | 2022 |
| yotta | Y | 10$^{24}$ | 1000000000000000000000000 | 1991 |
| zetta | Z | 10$^{21}$ | 1000000000000000000000 | 1991 |
| exa | E | 10$^{18}$ | 1000000000000000000 | 1975 |
| peta | P | 10$^{15}$ | 1000000000000000 | 1975 |
| tera | T | 10$^{12}$ | 1000000000000 | 1960 |
| giga | G | 10$^9$ | 1000000000 | 1960 |
| mega | M | 10$^6$ | 1000000 | 1873 |
| kilo | k | 10$^3$ | 1000 | 1795 |
| hecto | h | 10$^2$ | 100 | 1795 |
| deca | da | 10$^1$ | 10 | 1795 |
| — | — | 10$^0$ | 1 | — |
| deci | d | 10$^{−1}$ | 0.1 | 1795 |
| centi | c | 10$^{−2}$ | 0.01 | 1795 |
| milli | m | 10$^{−3}$ | 0.001 | 1795 |
| micro | μ | 10$^{−6}$ | 0.000001 | 1873 |
| nano | n | 10$^{−9}$ | 0.000000001 | 1960 |
| pico | p | 10$^{−12}$ | 0.000000000001 | 1960 |
| femto | f | 10$^{−15}$ | 0.000000000000001 | 1964 |
| atto | a | 10$^{−18}$ | 0.000000000000000001 | 1964 |
| zepto | z | 10$^{−21}$ | 0.000000000000000000001 | 1991 |
| yocto | y | 10$^{−24}$ | 0.000000000000000000000001 | 1991 |
| ronto | r | 10$^{−27}$ | 0.000000000000000000000000001 | 2022 |
| quecto | q | 10$^{−30}$ | 0.000000000000000000000000000001 | 2022 |
| Notes ↑ 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.

### Mathematics

* Decimal based on the number ten.
* Decagon a plane figure with ten sides
* Decahedron a polyhedron with ten faces

### Chemistry

* Decane, a hydrocarbon with 10 carbon atoms

### Biology

* Decapoda, an order of crustaceans with ten feet

### Religion

* The Decalogue, the Ten Commandments