Guide to Fundamental SI Units |
The foundation of modern metrology is the International System of Units (SI), which is used internationally to define the fundamental units of measurement. These are used to derive other units and are used to define other measurement units, such as may be used locally. |
Base Units |
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Parameter |
SI Unit |
Abbreviation |
Definition |
Time |
second |
s |
The duration of 9,192,631,770 cycles of radiation corresponding to a particular transition of the cesium-133 atom. |
Mass |
kilogram |
kg |
The mass of a cylinder of platinum iridium alloy kept in Paris, France. |
Electric Current |
Ampere |
A |
The current producing a force of 2*10-7 newtons per meter of length between two long wires 1 m apart in space. |
Thermodynamic Temperature |
Kelvin |
K |
1/273.16 of the thermodynamic triple point of water. |
Luminous Intensity |
candela |
cd |
The luminous intensity in a given direction of a source that emits monochromatic radiation at a frequency of 540*1012 Hertz, with a radiant intensity in that direction of 1/683 watts per steradian. |
Amount of Substance |
mole |
m |
The amount of substance in a system that contains as many elementary items as there are atoms in 0.012 kg of carbon 12. |
Length |
metre |
m |
The distance traveled by light in a vacuum in 1/299,792,458 s. |
Derivative Units |
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Parameter |
SI Unit |
Abbreviation |
Definition |
Electric Potential |
volt |
V |
W/A |
Frequency |
hertz |
Hz |
1/s |
Force |
newton |
N |
kg*m/s² |
Pressure |
pascal |
Pa |
N/m² |
Power |
watt |
W |
J/s |
Dose Equivalent |
sievert |
Sv |
m²/s² |
Electric Resistance |
ohm |
ohm |
V/A |
Quantity of Charge |
coulomb |
C |
A*s |
Electric Capacitance |
farad |
F |
C/V |
Conductance |
siemens |
S |
A/V |
Magnetic Flux |
weber |
Wb |
V*s |
Magnetic Flux Density |
tesla |
T |
Wb/² |
Inductance |
henry |
H |
Wb/A |
Celsius Temperature |
degree |
°C |
K |
Luminous Flux |
lumen |
lm |
cd*sr |
Illuminance |
lux |
lx |
lm/m² |
Activity |
becquerel |
Bq |
1/s |
Absorbed Dose |
gray |
Gy |
J/kg |
Work or Energy |
joule |
J |
N*m |
Supplementary Units | |||
Parameter |
SI Unit |
Abbreviation |
Definition |
Solid Angles |
steradian |
sr |
The solid angle with vertex at the center of a sphere that is subtended by an area of the spherical circle equal to that of a square with sides equal in length to the radius. |
Plane Angles |
radian |
rad |
A plane angle with vertex at the center of a circle that is subtended by an arc equal in length to the radius. |