The International System of Units (SI)

Table 1 The SI Base Units
Quantity Name Symbol Definition
length meter m “. . . the length of the path traveled by light in vacuum in 1/299,792,458 of a second.” (1983)
mass kilogram kg “. . . this prototype [a certain platinum–iridium cylinder] shall henceforth be considered to be the unit of mass.” (1889)
time second s “. . . the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom.” (1967)
electric current ampere A “. . . that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, and placed 1 meter apart in vacuum,would produce between these conductors a force equal to \(2\times10^{-7}\) newton per meter of length.” (1946)
thermodynamic temperature kelvin K “. . . the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.” (1967)
amount of substance mole mol “. . . the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of carbon-12.” (1971)
Table 2 Some SI Derived Units W/(m.K)
Quantity Name of Unit Symbol
area square meter \(m^2\)
volume cubic meter \(m^3\)
fequency hertz Hz \((s^{-1})\)
mass density (density) kilogram per cubic meter \(kg/m^3\)
speed, velocity meter per second m/s
angular velocity radian per second rad/s
acceleration meter per second per second \(m/s^2\)
angular acceleration radian per second per second \(rad/s^2\)
force newton N (kg.m/s^2)
pressure pascal \(Pa (N/m^2)\)
work, energy, quantity of heat joule J (N.m)
power watt W (J/s)
quantity of electric charge coulomb C (A.s)
potential difference, electromotive force volt V (W/A)
electric field strength volt per meter (or newton per coulomb) V/m (N/C)
electric resistance ohm \(\Omega (V/A)\)
capacitance farad F (A.s/V)
magnetic flux weber Wb (V.s)
inductance henry H (V.s/A)
magnetic flux density tesla T \((Wb/m^2)\)
magnetic field strength ampere per meter A/m
entropy joule per kelvin J/K
specific heat joule per kilogram kelvin J/(kg.K)
thermal conductivity watt per meter kelvin
radiant intensity watt per steradian W/sr