## SI Base Units

The International System of Units (SI) define the following base units

**Meter (m)**

The length of the path traveled by light in a vacuum during a time interval of 1/299 792 458 of a second.

**Kilogram (kg)**

Equal to the mass of the international prototype of the kilogram. The prototype is an alloy of 90% platinum and 10% iridium. It was manufactured in the 1880s and kept with its six official copies in a vault at the BIPM.

**Second (s)**

The base unit of time. It is the duration of 9 192 631 770 periods of radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium 133 atom.

**Ampere (A)**

A constant electric current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in a vacuum, would produce between these conductors a force equal to 2 × 10^{-7} newton per meter of length.

**Kelvin (K)**

The fraction 1/273.16 of the thermodynamic temperature of the triple point of water.

**Candela (cd)**

Unit for luminous intensity. A source that emits monochromatic radiation of frequency 540 × 10^{12} hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

**Mole (mol)**

Unit for quantity of matter. The amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon 12.

## SI Derived Units

Derived quantity |
Name |
Symbol |
Other symbol |
Base units |
---|---|---|---|---|

plane angle | radian | rad | - | m·m^{-1} = 1 |

solid angle | steradian | sr | - | m^{2}·m^{-2}=1 |

frequency | hertz | Hz | - | s^{-1} |

force | newton | N | - | m·kg·s^{-2} |

pressure, stress |
pascal | Pa | N/m^{2} |
m^{-1}·kg·s^{-2} |

energy, work, quantity of heat |
joule | J | Nm | m^{2}·kg·s^{-2} |

power, radiant flux |
watt | W | J/s | m^{2}·kg·s^{-3} |

electric charge, quantity of electricity |
coulomb | C | - | s·A |

electric potential, difference, electromotive force |
volt | V | W/A | m^{2}·kg·s^{-3}·A^{-1} |

capacitance | farad | F | C/V | m^{-2}·kg^{-1}·s^{4}·A^{2} |

electric conductance |
siemens | S | A/V | m-^{2}·kg^{-1}·s^{3}·A^{2} |

electric resistance | ohm | W | V/A | m^{2}·kg·s^{-3}·A^{-2} |

magnetic flux | weber | Wb | Vs | m^{2}·kg·s^{-2}·A^{-1} |

magnetic flux density | tesla | T | Wb/m^{2} |
kg·s^{-2}·A^{-1} |

inductance | henry | H | Wb/A | m^{2}·kg·s^{-2}·A^{-2} |

Celsius temperature | degree Celsius | °C | - | K |

luminous flux | lumen | lm | cd·sr | m^{2}·m^{-2}·cd = cd |

illuminance | lux | lx | lm/m^{2} |
m^{2}·m^{-4}·cd = m^{-2}·cd |

activity (of a radionuclide) | becquerel | Bq | - | s^{-1} |

absorbed dose, specific energy (imparted), kerma | gray | Gy | J/kg | m^{2}·s^{-2} |

dose equivalent | sievert | Sv | J/kg | m^{2}·s^{-2} |

catalytic activity | katal | kat | - | s^{-1}mol |

## SI Unit Prefixes

Derived quantity |
Name |
Symbol |
Other symbol |
Base units |
---|---|---|---|---|

plane angle | radian | rad | - | m·m^{-1} = 1 |

solid angle | steradian | sr | - | m^{2}·m^{-2}=1 |

frequency | hertz | Hz | - | s^{-1} |

force | newton | N | - | m·kg·s^{-2} |

pressure, stress |
pascal | Pa | N/m^{2} |
m^{-1}·kg·s^{-2} |

energy, work, quantity of heat |
joule | J | Nm | m^{2}·kg·s^{-2} |

power, radiant flux |
watt | W | J/s | m^{2}·kg·s^{-3} |

electric charge, quantity of electricity |
coulomb | C | - | s·A |

electric potential, difference, electromotive force |
volt | V | W/A | m^{2}·kg·s^{-3}·A^{-1} |

capacitance | farad | F | C/V | m^{-2}·kg^{-1}·s^{4}·A^{2} |

electric conductance |
siemens | S | A/V | m-^{2}·kg^{-1}·s^{3}·A^{2} |

electric resistance | ohm | W | V/A | m^{2}·kg·s^{-3}·A^{-2} |

magnetic flux | weber | Wb | Vs | m^{2}·kg·s^{-2}·A^{-1} |

magnetic flux density | tesla | T | Wb/m^{2} |
kg·s^{-2}·A^{-1} |

inductance | henry | H | Wb/A | m^{2}·kg·s^{-2}·A^{-2} |

Celsius temperature | degree Celsius | °C | - | K |

luminous flux | lumen | lm | cd·sr | m^{2}·m^{-2}·cd = cd |

illuminance | lux | lx | lm/m^{2} |
m^{2}·m^{-4}·cd = m^{-2}·cd |

activity (of a radionuclide) | becquerel | Bq | - | s^{-1} |

absorbed dose, specific energy (imparted), kerma | gray | Gy | J/kg | m^{2}·s^{-2} |

dose equivalent | sievert | Sv | J/kg | m^{2}·s^{-2} |

catalytic activity | katal | kat | - | s^{-1}mol |

## The US Customary System of Measures

The following are the English System of measurement

**Length**

12 inches = 1 foot

3 feet = 1 yard

220 yards = 1 furlong

8 furlongs = 1 mile

5 280 feet = 1 mile

1 760 yards = 1 mile

**Area**

144 square inches = 1 square foot

9 square feet = 1 square yard

4 840 square yards = 1 acre

640 acres = 1 square mile

1 square mile = 1 section

36 sections = 1 township

**Volume**

1,728 cubic inches = 1 cubic foot

27 cubic feet = 1 cubic yard

**Mass**

437.5 grains = 1 ounce

16 ounces = 1 pound

14 pounds = 1 stone

100 pounds = 1 hundredweight

20 hundredweights = 1 ton

**Capacity (Dry)**

16 fluid ounces = 1 pint

2 pints = 1 quart

8 quarts = 1 peck

4 pecks = 1 bushel

**Capacity (Liquid)**

4 gills = 1 pint

2 pints = 1 quart

4 quarts = 1 gallon

**Apothecaries' Measures**

60 minims = 1 fluid dram

8 fluid drams = 1 fluid ounce

16 fluid ounces = 1 pint

**Apothecaries' Weights**

20 grains = 1 scruple

3 scruples = 1 dram

8 drams = 1 ounce

**Troy Weights**

24 grains = 1 pennyweight

20 pennyweights = 1 ounce