The theoretical mean molar electrostriction volume of electrolytic solvents, Delta V-el(solvent), was calculated from their properties: the relative pressure derivatives of the density (the compressibility) and permittivity and their second pressure derivatives. The molar electrostriction caused by ions at infinite dilution was taken as the differences of their standard partial molar volumes in the solution and their intrinsic volumes: Delta V-el(ion) = V-infinity(ion) - V-in(ion). The ratio n(infinity) = Delta V-el(ion)/Delta V-el(solvent) then represents the solvation number of the ion in the solvent at infinite dilution. Similarly, from the molar volume change on ion pair formation, Delta V-ip, the ratio Delta n(ip) = Delta V-ip/Delta V-el(solvent) represents the number of solvent molecules released thereby. These values were tabulated for those solvents, ions, and ion pairs for which the relevant information could be found, the extension to nonaqueous solvents not having been attempted previously.