2.03 Derived Units

Base quantities


Base quantities are simply the physical properties that are measured by each of the base SI Units.

Derived units


All of the other SI units are derived from the base units. This means that all of the other SI units are basically different combinations of base units which have been given their own special names and symbols.
e.g Pressure is measured in units called Pascals and has the symbol Pa. However a Pascal is equivalent to a particular combination of base units. i.e. 1Pa = 1 kg/m.s2.

Table of derived SI units

Physical quantity Name of unit Symbol Expressed in base units
Frequency Hertz Hz 1/s
Force Newton N m.kg/s2
Work (Energy) Joule J m2.kg/s2
Pressure Pascal Pa kg/m.s2
Power Watt W m2.kg/s3
Electric charge Coulomb C A.s
Electric potential Volt V m2.kg/s3.A
Electric capacitance Farad F s2.s2.A2/m2.kg
Electric resistance, reactance Ohm Ω m2.kg/s3.A2
Electric conductance Siemens S s3.A2/m2.kg
Magnetic flux Weber Wb m2.kg/s2.A
Magnetic induction Tesla T kg/s2.A
Inductance Henry H m2.kg/s2.A2
Luminous flux Lumen lm cd.sr
Illuminance lux lx cd.sr/m2

Derived quantities


Derived quantities are simply the physical properties that are measured by each of the units in the table above