## Metric Prefixes

The metric system is a decimalised system of measurement. It is known as the International System of Units or Système international (SI), and is recognised the world over. The metric prefixes listed below precede a basic unit of measurement to indicate a multiple (or sub-multiple) of that unit.

Value | Prefix Name | Prefix Symbol |
---|---|---|

10^{24} | yotta- | Y |

10^{21} | etta- | Z |

10^{18} | exa- | E |

10^{15} | peta- | P |

10^{12} | tera- | T |

10^{9} | giga- | G |

10^{6} | mega- | M |

10^{3} | kilo- | k |

10^{2} | hecto- | h |

10 | deca- | da |

10^{−1} | deci- | d |

10^{−2} | centi- | c |

10^{−3} | milli- | m |

10^{−6} | micro- | μ |

10^{−9} | nano- | n |

10^{−12} | pico- | p |

10^{−15} | femto- | f |

10^{−18} | atto- | a |

10^{−21} | zepto- | z |

10^{−24} | yocto- | y |

## Fundamental Units

These are the seven basic SI units from which all other physical quantities are defined.

Quantity Name | Unit Name | Unit Symbol |
---|---|---|

time | second | s |

length | metre | m |

mass | kilogram | kg |

electric current | ampere | A |

thermodynamic temperature | kelvin | K |

luminous intensity | candela | cd |

amount of substance | mole | mol |

The *Celsius* temperature scale is equivalent to the Kelvin temperature scale, with 0 °C = 273.15 K.

## Derived Units

These units are derived from various combinations (products, quotients and powers) of the fundamental units.

Quantity | Name | Symbol | SI Base Units | Other SI Units |
---|---|---|---|---|

acceleration | m∙s^{−2} | |||

acceleration, angular | rad∙s^{−2} | |||

angle, plane | radian | rad | [dimensionless] | |

angle, solid | steradian | sr | [dimensionless] | |

area | m^{2} | |||

capacitance | farad | F | kg^{−1}∙m^{−2}∙s^{4}⋅A^{2} | C∙V^{−1} |

catalytic activity | katal | kat | mol∙s^{−1} | |

concentration | mol∙m^{−3} | |||

density | ρ | kg∙m^{−3} | ||

electric charge | coulomb | C | s∙A | |

electric field strength | kg∙m∙s^{−3}∙A^{−1} | N∙C^{−1}, V∙m^{−1} | ||

electrical conductance | siemens | S | kg^{−1}∙m^{−2}∙s^{3}∙A^{2} | A∙V^{−1}, Ω^{−1} |

electrical potential | volt | V | kg∙m^{2}∙s^{−3}∙A^{−1} | W∙A^{−1}, J∙C^{−1} |

energy | joule | J | kg∙m^{2}∙s^{−2} | N∙m |

entropy | kg∙m^{2}∙s^{−2}∙K^{−1} | J∙K^{−1} | ||

force | newton | N | kg∙m∙s^{−2} | |

frequency | hertz | Hz | s^{−1} | |

heat | joule | J | kg∙m^{2}∙s^{−2} | N∙m |

heat capacity | kg∙m^{2}∙s^{−2}∙K^{−1} | J∙K^{−1} | ||

illuminance | lux | lx | cd∙sr⋅m^{−2} | |

impedance | ohm | Ω | kg∙m^{2}∙s^{−3}∙A^{−2} | V∙A^{−1} |

inductance | henry | H | kg∙m^{2}∙s^{−2}∙A^{−2} | V∙s∙A^{−1} |

irradiance | kg∙s^{−3} | W∙m^{−2} | ||

luminance | cd∙m^{−2} | |||

luminous flux | lumen | lm | cd∙sr | |

magnetic flux | weber | Wb | kg∙m^{2}∙s^{−2}∙A^{−1} | V∙s |

magnetic flux density | tesla | T | kg∙s^{−2}∙A^{−1} | V∙s∙m^{−2} |

moment of inertia | kg∙m^{2} | |||

momentum | kg∙m∙s^{−1} | N∙s | ||

momentum, angular | kg∙m^{2}∙s^{−1} | N∙m∙s | ||

permeability | kg∙m∙s^{−2}∙A^{−2} | H∙m^{−1} | ||

permittivity | kg^{−1}∙m^{−3}∙s^{4}∙A^{2} | F∙m^{−1} | ||

power | watt | W | kg∙m^{2}∙s^{−3} | J∙s^{−1} |

pressure | pascal | Pa | kg∙m^{−1}∙s^{−2} | N∙m^{−2} |

radiant intensity | kg∙m^{2}∙s^{−3}∙sr^{−1} | W∙sr^{−1} | ||

radiation dose | gray | Gy | m^{2}∙s^{−2} | J∙kg^{−1} |

radiation dose equivalent | sievert | Sv | m^{2}∙s^{−2} | J∙kg^{−1} |

radioactivity | becquerel | Bq | s^{−1} | |

resistance | ohm | Ω | kg∙m^{2}∙s^{−3}∙A^{−2} | V∙A^{−1} |

specific heat capacity | m^{2}∙s^{−2}∙K^{−1} | |||

specific volume | kg^{−1}∙m^{3} | |||

stress | pascal | Pa | kg∙m^{−1}∙s^{−2} | N∙m^{−2} |

surface density | kg∙m^{−2} | |||

thermal conductivity | kg∙m∙s^{−3}∙K^{−1} | W∙m^{−1}∙K^{−1} | ||

torque | kg∙m^{2}∙s^{−2} | N∙m | ||

velocity | m∙s^{−1} | |||

velocity, angular | rad∙s^{−1} | |||

viscosity, dynamic | kg∙m^{−1}∙s^{−1} | N∙s∙m^{−2}, Pa∙s | ||

viscosity, kinematic | m^{2}∙s^{−1} | |||

volume | m^{3} | |||

wave number | m^{−1} | |||

work | joule | J | kg∙m^{2}∙s^{−2} | N∙m |

## Non-SI Units

These units are often used in conjunction with SI units.

Quantity | Name | Symbol | Equivalent Value |
---|---|---|---|

area | hectare | ha | 1 ha = 10^{4} m^{2} |

energy | electronvolt | eV | 1 eV = 1.602176634×10^{−19} J |

length | astronomical unit | au | 1 au = 149,597,870,700 m |

light year | ly | 1 ly = 9,460,730,472,580,800 m | |

parsec | pc | 1 pc = (648,000/π) au | |

mass | tonne or metric ton | t | 1 t = 1000 kg |

plane/phase angle | degree | ° | 1° = (π/180) rad |

minute | ′ | 1′ = (1/60)° = (π/10,800) rad | |

second | ″ | 1″ = (1/60)′ = (π/648,000) rad | |

pressure | bar | bar | 1 bar = 100,000 Pa |

time | day | d | 1 d = 24 hr = 1440 min = 86,400 s |

hour | hr | 1 hr = 60 min = 3,600 s | |

minute | min | 1 min = 60 s | |

volume | litre | l, L | 1 L = 10^{3} cm^{3} = 10^{−3} m^{3} |