According to the International System of Units, the basic units are the meter (m), the kilogram (kg), the second (s), the ampere (A), the Kelvin (K), the candela (cd) and the mole (mol). These units are commonly found in technical applications, including electrical or control applications. All other units are derived from these seven units.
1 kilogram (1 kg) is the mass of the international prototype of the kilogram which is kept at the Bureau International des Poids et Mesures in Sèvres near Paris.
1 meter (1 m) is the length of the path traveled by light in a vacuum during a time interval of 1/299,792,458 of a second.
1 second (1 s) is 9,162,631,770 times the period of the radiation corresponding to the transition between the two hyperfine structure levels of the fundamental state of atoms of the nuclide 133Cs.
1 kelvin (1 K) is the 1/273.15th part of the thermodynamic temperature of the triple point of water.
1 candela (1 cd) is the luminous intensity in a given direction of a source that emits monochromatic radiation of frequency 540 x 1012 hertz and has a radiant intensity in that same direction of 1/683 watt per steradian (unit solid angle).
1 ampere (1 A) is the intensity of an electric current, non-varying with time, whereupon when flowing through two conductors of negligibly small circular cross-section arranged parallel to one another at a distance of 1 m in a vacuum, an electrodynamic force of 2 x 10–7 N per m of conductor length is exerted between these.
1 mole (1 mol) is the amount of substance in a system that contains as many elementary entities as there are atoms in 12/1000 kilogram of carbon 12.
1 volt (1 V) is equal to the electrical current between two points in a thread-like, homogeneous conductor of even temperature carrying a current of 1 A when the power dissipated between the points is one watt. The resistance of this conductor is 1 Ω.
1 joule (1 J) is equivalent to the work done when a force of one newton moves its point of application one meter in the direction of the force.
1 Watt (1 W) is equal to one joule (1 J) of work performed per second.
Source: Rittal “Technical Aspects of Enclosures” handbook