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SI Units & Symbols
- chart or table of the SI or System International units with the SI symbols used along with the quantities they measure or define.
Units, symbols & constants pages include:
• SI base units
• SI units & symbols
• SI metric prefixes
• Electronic unit definitions
• Metric / Imperial conversion chart
It is standard practice to use abbreviations to define the various SI units. The SI unit symbols are normally widely recognised, although some are less common.
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.
For further use, only the unit symbol need be used.
SI unit symbol 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 and the associated SI symbols
| 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 |
Other popular reference pages & tables . . . . . |
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| • dBm / Watts table | • Trig functions | • Fourier series | • Constants |
| • SI base units | • SI prefixes | • Sidereal time | • Greek letters |
| • Resistivity | • Physical constants | • Capacitance | • Circuit symbols |