The numerical solution of the Clausius‐Mossotti problem for the permittivity of a suspension of perfectly conducting spheres in a cubic array is presented for sc, fcc, and bcc lattices. The results apply to electrical permittivity, magnetic permeability, electrical and thermal conductivity, and particle diffusivity. The calculations are compared with the Clausius‐Mossotti relation. Rayleigh’s equation is corrected and compared with the numerical results. A simple interpolation formula for the permittivity of a medium of perfectly conducting spheres in a simple cubic lattice is found to give an excellent approximation at all volume ratios.