Graphs of the total radius (the distance between an anionic nuclei and a cationic nuclei in a crystal) of sodium halides and alkali metal fluorides versus total limiting equivalent conductivities were plotted. For the hard ions Na + and F − , whose behaviour approaches a hard spherical model, it was determined that radii values could be obtained using differences in limiting equivalent conductivities and ionic crystal data. From the determined radii of sodium and fluoride ions and known crystal data, radii of other alkali metal halides were calculated.