A generalization is made of the methods for calculating geometric parameters of a high-capacity holographic digital memory. The generalization is based on the principles of geometric optics and theory of diffraction. Optimal relationships are obtained between the geometric parameters of the memory. These relationships can be used to calculate the maximum total capacity for given dimensions and, conversely, the minimum dimensions for a given total capacity (this ensures also the maximum information density in the hologram). Examples of calculations of geometric parameters of optimized memories of this kind are given.