## SI Units – Système International d’Unités

## the modern scientific system of units

### + – + – + – + – + – + – + – + – + – +– + – +– + – + – + – + – + – + – + – +

### SI Units, Other Units or SI Prefixes

**SI Units**

Unit |
Symbol |
Quantity |

ampere |
A |
electric current |

becquerel | Bq | radioactivity |

candela |
cd |
luminous intensity |

coulomb | C | electric charge, electric flux |

farad | F | electrical capacitance |

gray | Gy | absorbed dose of ionizing radiation |

henry | H | inductance |

hertz | Hz | frequency |

joule | J | work, energy and heat |

katal | kat | catalytic activity |

kelvin |
K |
thermodynamic temperature |

kilogram |
kg |
mass |

lumen | lm | luminous flux |

lux | lx | illuminance |

metre |
m |
length |

mole |
mol |
amount of substance |

newton | N | force |

ohm | Ω | electric resistance, impedance, reactance |

pascal | Pa | pressure, stress |

radian | rad | plane angle |

second |
s |
time |

siemens | S | electrical conductance |

sievert | Sv | radiation dose equivalent |

steradian | sr | solid angle |

tesla | T | magnetic flux density, magnetic induction, magnetic field strength |

volt | V | electromotive force, electric potential, potential difference |

watt | W | power, radiant flux |

weber | Wb | magnetic flux |

**Base SI units are shown in red**, all other units are derived

**Other Units**

Unit |
Symbol |
Quantity / Notes |

ångström | Å | wavelength of light, ultraviolet rays, X-rays, molecular and atomic distances |

are | a | land measure = 100 sq metres |

astronomical unit | au | the earth’s mean distance from the sun, about 92.9 million miles |

bar | bar | atmospheric pressure |

barn | b | effective cross-sectional area of a nucleus for the capture of neutrons |

bel | B | relationship between two power levels |

curie | Ci | former unit of radioactivity |

day | d | time = 24 hours |

degree | ° | angle = 1/360 of a circle = 60 minutes |

degree Celsius | ºC | temperature = 1 kelvin |

electronvolt | eV | energy acquired by an electron when accelerated by a potential of one volt |

hectare | ha | land measure = 100 ares or 10000 sq metres |

hour | h | time = 1/24 of a day = 60 minutes |

knot | 1 nautical mile per hour | |

litre | L | volume = 1 cubic decimetre = 1000 cubic centimetres |

metric ton | see tonne | |

minute | min | time = 1/60 of an hour = 60 seconds |

minute | ‘ | angle = 1/60 of a degree = 60 seconds |

nautical mile | one minute of latitude measured along a meridian | |

neper | Np | ratio of two currents, two voltages, etc |

oersted | Oe | magnetic field strength |

rad | rad | former unit of absorbed radiation dose |

rem | rem | former unit of radiation dosage |

roentgen / röntgen | R | dose of X-rays or gamma rays |

second | ” | angle = 1/60 of a minute |

tonne / metric ton | t | mass = 1000 kilograms |

unified atomic mass unit | u | approximate mass of a hydrogen atom, a proton, or a neutron |

**SI Prefixes**

Prefix |
Symbol |
Exponent (base 10) |

yotta | Y | 24 |

zetta | Z | 21 |

exa | E | 18 |

peta | P | 15 |

tera | T | 12 |

giga | G | 9 |

mega | M | 6 |

kilo | k | 3 |

hecto | h | 2 |

deca | da | 1 |

0 | ||

deci | d | -1 |

centi | c | -2 |

milli | m | -3 |

micro | µ | -6 |

nano | n | -9 |

pico | p | -12 |

femto | f | -15 |

atto | a | -18 |

zepto | z | -21 |

yocto | y | -24 |

Created 11 April 2010