# electrical conductance

Electrical conductance (*G*) is the reciprocal of electrical
resistance (i.e., 1/*R*). The SI
unit of conductance is the siemens,
formerly (in MKS units) called the mho or reciprocal ohm. See also conductivity.

Electrical conductance (symbolized by *G*) is a useful concept especially
when dealing with parallel DC (direct current) circuits. For a similar reason,
the reciprocal of the impedance, defined
as the admittance, is useful in handling
parallel AC (alternating current) circuits. In the case of parallel AC circuits, *G* reduces to 1/*R* when purely resistive elements are present.
In the general case when there are both resistive and reactive elements,
the expression for *G* is *R*/(*R*^{2} + *X*^{2}),
where *X* is the reactance.