# SI Units, Symbols & Abbreviations

### The chart below gives the standard abbreviations and symbols for the major quantities measured using SI units - the International System of Units.

**SI, International System of Units Includes:**

SI base units
SI units & symbols
SI / metric prefixes
Unit definitions
SI (metric) / Imperial conversion

There are many abbreviations used to denote different measurements and quantities. The chances are that any scientific measurement or quantity will be measured using SI Units - the International System of Units.

There are many standard abbreviations and symbols used with these quantities. The SI, System International units, symbols and abbreviations are well defined and documented and provide the basis for the way most scientific quantities (as well as many others) are quoted and measured.

The SI unit symbols for quantities such as current, voltage and the like, are very common, and within electrical or electronic circles.

However when an unfamiliar unit symbol is first used within a paper or other document, it should be followed by its name in parentheses. In this way readers who may not be familiar with the particular unit symbol may be able to understand it.

## SI unit symbol & abbreviation usage

When writing SI unit symbols, they are written in lower case except for cases where the unit is derived from a proper name, or in the very few cases where the abbreviation is not formed from a letter.

The definition for methods of writing SI symbols states that the symbols for the units should not be followed by a period / full stop. In other words a current of ten amperes is written 10A, and not 10A., although punctuation for sentences still applies.

When a compound unit SI unit symbols is made by multiplying two or more other units, its overall symbol should consist of the symbols for the separate units joined by dots which are raised, i.e. ⋅ . However the raised dot, may be omitted in the case of familiar compound unit symbols.

For example both V ⋅ s and V s are acceptable.

## Table of the SI units, symbols, & abbreviations

SI Units & SI Unit Symbols |
||
---|---|---|

SI Unit Name | SI Unit Symbol | Quantity measured |

ampere | A |
Electric current |

ampere per meter | A/m |
Magnetic field strength |

ampere per square meter | A/m^2 |
Current density |

becquerel | Bq s^-1 |
Activity - of radionuclide |

candela | cd |
Luminous intensity |

candela per square metre | cd/m^2 |
Luminance |

coulomb | C s ⋅ A |
Electric charge, quantity of electricity |

coulomb per cubic metre | C/m^3 |
Electric charge density |

coulomb per kilogram | C/kg |
Exposure (x rays & gamma rays) |

coulomb per square metre | C/m^2 |
Electric flux density |

cubic metre | m^3 |
Volume |

cubic metre per kilogram | m^3/kg |
Specific volume |

degree Celsius | °C |
Celsius temperature |

farad | F C/V |
Capacitance |

farad per metre | F/m |
Permittivity |

gray | Gy |
Absorbed dose, specific energy imparted, absorbed dose index |

gray per second | Gy/s |
Absorbed dose rate |

henry | H Wb/A |
Inductance |

henry per metre | H/m |
Permeability |

hertz | Hz s^-1 |
Frequency |

joule | J N⋅m |
Energy, work, quantity of heat |

joule per cubic metre | J/m^3 |
Energy density |

joule per kelvin | J/K |
Heat capacity, entropy |

joule per kilogram | J/kg |
Specific energy |

joule per kilogram kelvin | J/(kg⋅K) |
Specific heat capacity |

joule per mole | J/mol |
Molar energy |

joule per mole kelvin | J/(mol⋅K) |
Molar heat capacity, molar entropy |

kelvin | K |
Absolute temperature, sometimes referred to as thermodynamic temperature |

kilogram | kg |
Mass |

kilogram per cubic metre | kg/m^3 |
Density, mass density |

lumen | lm |
Luminous flux |

lux | lx lm/m^2 |
Illuminance |

metre | m |
Length |

metre per second | m/s |
Speed, velocity |

metre per second squared | m/s^2 |
Acceleration |

mole | mol |
Amount of substance |

mole per cubic metre | mol/m^3 |
Concentration |

newton | N |
Force |

newton metre | N⋅m |
Moment of force |

newton per metre | N/m |
Surface tension |

ohm | Ω V/A |
Electric resistance |

pascal | Pa N/m^2 |
Pressure, stress |

pascal second | PA ⋅ s |
Dynamic viscosity |

radian | rad |
Plane angle |

radian per second | rad/s |
Angular velocity |

radian per second squared | rad/s^2 |
Angular aceleration |

second | s |
Time or time interval |

siemens | S A/V |
Electric conductance (1/electric resistance) |

sievert | Sv |
Dose equivalent (index) |

square metre | m^2 |
Area |

steradian | sr |
Solid angle |

tesla | T Wb/m2 |
Magnetic flux density |

volt | V W/A |
Electrical potential or potential difference, electromotive force |

volt per metre | V/m |
Electric field strength |

watt | W J/s |
Power |

watt per metre kelvin | W/(m⋅K) |
Thermal conductivity |

watt per square metre | W/m^2 |
Power density, heat flux density, irrandiance |

watt per square metre steradian | W ⋅ m^-2 ⋅ sr^-1 |
Radiance |

watt per steradian | W/sr |
Radiant intensity |

weber | Wb &nbnsp; V ⋅ s |
Magnetic flux |

The table above gives some of the most commonly used SI symbols, units and abbreviations which are seen in scientific and engineering applications.

**More Basic Concepts:**

Voltage
Current
Resistance
Capacitance
Power
Transformers
RF noise
Decibel, dB
Q, quality factor
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