Conductance is a measure of the ability of a material to conduct electricity. In a direct current (DC) circuit, it is the reciprocal of electrical resistance. For example, a conductor of resistance R has a conductance of 1/R. In an alternating (AC) circuit, it is the resistance divided by the square of impedance (the opposition of a circuit to the passage of a current); G = R /Z ². The SI unit of conductance is the siemens.