The SI system consists of 7 base units, and a number of derived units that have special names, e.g. watt. Any of the base units or derived units can be prefixed by multipliers, see our page on SI Prefixes for a list of common multipliers.

Unit | Symbol | Property Measured | Definition |

becquerel | BQ | radioactivity | One becquerel is defined as one spontaneous nuclear transition per second. |

coulomb | C | electric charge | The amount of charge transported through any cross section of a conductor in one second by a constant current of one ampere. It is equivalent to the amount of charge on about 6,241,510,000,000,000,000 electrons. |

degree Celsius | °C | temperature | Temperature on the Celsius scale is the temperature on the Kelvin scale minus 273.15 |

farad | F | capacitance | A capacitor has a capacitance of 1 farad if a charge of 1 coulomb increases the potential difference between its plates by 1 volt. |

gray | Gy | absorbed dose | One gray is the quantity of ionising radiation that, absorbed in a mass of 1 kilogram, would impart to it 1 joule of energy. |

henry | H | inductance | The self or mutual inductance of a closed loop is 1 henry if a current of 1 ampere gives rise to a magnetic flux of 1 weber. |

hertz | Hz | frequency | The number of periods of a periodic phenomenon's frequency in 1 second. |

joule | J | energy | The energy expended when the point of application of a force of 1 newton is displaced 1 meter in the direction of the force. |

katal | kat | catalytic activity | One katal is that catalytic activity which will raise the rate of reaction by one mole per second in a specified assay system. |

lumen | lm | luminous flux | One lumen is the luminous flux emitted within a solid angle of 1 steradian by a point source with an intensity of 1 candela. |

lux | lx | illuminance | One lux is 1 lumen per square meter. |

newton | N | force | A newton is that force which, applied to a mass of 1 kilogram, gives it an acceleration of 1 meter per second per second. |

ohm | Ω | electrical resistance | The resistance of a circuit in which a potential difference of one volt produces a current of one ampere |

pascal | Pa | pressure | One pascal is the pressure resulting from a force of 1 newton acting uniformly over an area of 1 square meter. |

siemens | S | electric conductance | A conductor has a conductance of 1 siemens if an electrical potential difference of 1 volt produces a 1-ampere current in it. The reciprocal of resistance. |

sievert | Sv | dose equivalent | A sievert of radiation is the amount of any kind of radiation which would cause the same amount of biological damage in a human being as would result from absorbing 1gray of X rays. |

tesla | T | magnetic flux density | One tesla is one weber of magnetic flux per square meter of circuit area. |

volt | V | electrical potential | One volt is the potential difference between two points on a conductor when the current flowing is one ampere and the power dissipated between the points is one watt. |

watt | W | power | A watt is the power which in one second gives rise to energy of one joule. |

weber | Wb | magnetic flux | One weber is the magnetic flux which, linking a circuit of one turn, would produce in it an electromotive force of 1 volt if it were reduced to zero at a uniform rate in 1 second. |

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