This work proposed to determine the mean dispersion factor, < αC > , which is related to the relative photoelastic dispersion coefficient of a photoelastic material, subjected to consecutive external stresses, by means of a direct computational method associated with error theory. An important feature of photoelasticity, related to the light wavelength, is the photoelastic dispersion coefficient, which is determined in traditional methods by indirect statistical processes, as it depends on refractive indices, which are difficult to determine in photoelastic materials. Therefore, finding an alternative form to determine this coefficient is necessary and can help in the processes that involve the use of photoelasticity. The mean dispersion factor obtained was < αC > = (8,90 ± 0,42) x 10-5, which works as a system calibrator to allow the determination of the photoelastic dispersion coefficient of photoelastic materials by photoelasticity, with greater accuracy.