Under impulse conditions, very fast voltage pulses are applied to a transformer. These contain high-frequency components, eliciting capacitative effects that are absent at normal operating frequencies. Thus, in order to simulate the behavior of a transformer under impulse conditions, capacitances must be determined for use in circuit or traveling wave models. This chapter employs an energy method to determine the capacitance or, in general, the capacitance matrix. This method is a generalization of the method used by Stein to determine the disk capacitance of a disk embedded in a winding of similar disks. It utilizes a continuum model of a disk so that disks having many turns are contemplated. The chapter compares capacitances determined in this manner with capacitances determined using a conventional approach. The chapter presents a simple analytic formula for calculating the disk capacitance with a variable number of wound-in-shield turns. Since this formula rests on certain assumptions, a detailed circuit model is developed to test these assumptions.