A method of estimating an electrical capacitance of a circuit component is carried out by decomposing the capacitance into a sum of terms associated with respective contributions from a central part and peripheral parts of the component. A component to which the method can be applied comprises two rectangular conducting plates placed parallel to each other. One of the two plates is greater than the other. The component furthermore includes two different dielectrics. A first dielectric covers the large plate and separates the two plates, and a second dielectric surrounds the first plate and the first dielectric. A method of defining a dimension of a capacitor is also presented.