The property of a conductor or system of conductors that describes its ability to store electric charge. The capacitance (C) is given by Q/V, where Q is stored charge on one conductor and V the potential difference between the two conductors (or between a single conductor and earth); it is measured in farads, although microfarads are frequently a more convenient unit for practical purposes.

An isolated sphere has a capacitance of 4πε‎r, where r is the radius and ε‎ the permittivity of the medium surrounding it. Capacitance is more commonly applied to systems of conductors (or semiconductors) separated by insulators (see capacitor).