Guide to Fundamental SI Units

Base Units

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

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

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.