The property of an isolated conductor or a set of conductors and insulators whereby it stores electric charge. A charge of Q coulombs will increase the voltage of an isolated conductor by V volts. The capacitance is defined as the ratio Q/V and is determined by the size and shape of the conductor. It is constant for a given isolated conductor.

If the isolated conductor is placed near a second conductor or a semiconductor but is separated from it by air or some other insulator, the system forms a capacitor. An electric field is produced across the system and the potential difference between the conductors is determined by this field. The capacitance, C, is defined as the ratio of the charge on either conductor to the potential difference between them. See also mutual capacitance; impedance; series; parallel.