# SI Units & Symbols

### In this section

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
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
F     C/V
Capacitance
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
Plane angle
Angular velocity
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
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
W ⋅ m^-2 ⋅ sr^-1
W/sr
weber
Wb &nbnsp;   V ⋅ s
Magnetic flux

### Other popular tutorials

Sven Etzold | U-blox
Gladys West - Pioneer of GPS
GPS and GNSS positioning technology is such an integral part of our lives today that we rarely stop to think about where it all came from. When we do, we usually picture men in white shirts and dark glasses hunched over calculators and slide rules. In fact, one of the early pioneers behind GPS and GNSS technology was Gladys West - a black woman.

Forthcoming Events

. . . . More Events

##### Channels
Radio-Electronics.com is operated and owned by Adrio Communications Ltd and edited by Ian Poole. All information is © Adrio Communications Ltd and may not be copied except for individual personal use. This includes copying material in whatever form into website pages. While every effort is made to ensure the accuracy of the information on Radio-Electronics.com, no liability is accepted for any consequences of using it. This site uses cookies. By using this site, these terms including the use of cookies are accepted. More explanation can be found in our Privacy Policy