It is well known that the Sommerfeld screening parameters sigma ₁ and sigma ₂ for a spin doublet of levels can only be calculated if the individual energies of the two members of the doublet are known. In several cases, the resolution of the experimental method for finding the energies has proved insufficient and so only the energy of the unresolved doublet of levels has been reported. A new method has been developed for calculating these parameters for a spin doublet of levels by using the unresolved experimental energy values given by Bearden et al (1967). The results of the authors' calculations are presented. It is found that the energy values calculated by using these parameters in the Sommerfeld energy expression are in very good agreement with resolved experimental energy values of the individual components of different spin doublets.