Those units which are derived from the basic units of SI system are known as Derived units. For example: – the units of area are m^{2}, which are derived from the basic units of length i.e. m.

It is most often we find the basic SI units not of convenient size for the measurement being done. For example: – m will be quite a bigger unit for expressing the length of a paper but too small for the distance between two cities. For this reason only, we use Subsidiary units confined to +ive and –ive powers of 10 times the basic SI unit.

**The following table contains the Subsidiary units being used.**

Prefix | Symbol of Prefix | Scientific Notation |

atto | a | 10^{-18} |

femto | f | 10^{-15} |

pico | p | 10^{-12} |

nano | n | 10^{-9} |

micro | µ | 10^{-6} |

milli | m | 10^{-3} |

centi | c | 10^{-2} |

deci | d | 10^{-1} |

deca | da | 10^{1} |

Hector | h | 10^{2} |

kilo | k | 10^{3} |

mega | M | 10^{6} |

giga | G | 10^{9} |

tera | T | 10^{12} |

peta | P | 10^{15} |

exa | E | 10^{18} |

**The following table contains some commonly used Derived Units: –**

Symbol | Meaning | SI Unit |

A | Area | m2 |

V | Volume | m3 |

Ρ | Density | kg m-3 |

v | Velocity | m s-1 |

a | Acceleration | m s-2 |

F | Force | newton(N)= kg m s-2 |

p | Pressure | pascal(Pa)= N m-2 |

E | Energy | J=Nm kg m2 s-2 |

k | Force constant | N m-1 |

S | Electric conductivity | Ω-1 m-1 |

q | Electric charge | C(coulomb) |

µ | Dipole moment | C m |

Γ | Frequency | s-1 (Hz) |

V | Potential difference | V(volt) |

w | Power | W(watt) |

C | Capacitance | f(farad) |