The capacitance of a parallelplate capacitor or condenser is given in SI units by where is the area of each plate is the spacing between plates is the dielectric constant relative permittivity and is the permittivity of free space faradmeter If is expressed in and in then microfarads Capacitance determines the quantity of positive and negative charges that can be held on the plates by a voltage such that In an airgap capacitor in which there is no dielectric layer