For a given medium and wave and path lengths of incident light, the relationship was experimentally investigated among the intensity of transmitted light, the suspension concentration of particles and the median size on particle volume basis. The numerical correlations were examined and an approximate equation was proposed over a wider range of concentrations up to about 3 vol.%. This expression was found to be valid not only for uniformly sized particles but also for mixtures of different particle sizes as compared with the previous equations for low concentration of particles of uniform size.