Fractional void volume and specific geometrical surface of tower packings are important quantities for mass transfer operations. Regular packings of cylindric rings (Raschig rings, Pall rings) yield a maximum of specific geometrical surface and a minimum of fractional void volume. These limiting values have been calculated here in a fundamental way. Using the actual fractional void volume of a random packing the real value of the specific geometrical surface may be simply calculated. Comparisons between calculated values and results from literature and own measurements are presented.