For a separation between
conductors of the order of 1 cm or so, this field corresponds to a potential
difference of 3 × 104 V between the conductors Thus, for a capacitor to
store a large amount of charge without  leaking, its capacitance should
be high enough so that the potential difference and hence the electric
field do not exceed the break-down limits Put differently, there is a limit
to the amount of charge that can be stored on a given capacitor without
significant leaking In practice, a farad is a very big unit; the most common
units are its sub-multiples 1 mF = 10–6 F, 1 nF = 10–9 F, 1 pF = 10–12 F,
etc