In this work, a complex dielectric transformation of UV-vis diffuse reflectance spectra is proposed to estimate the optical band-gap energies of an array of materials classified as semi-conductors, conductors and insulators and the results are compared with the more common Kubelka-Munk (K-M) transformation. The results show a close match between the proposed method and the Tauc model based on the K-M transformation within ca. 0.16-7.07% variation. The proposed method based on the well-established dielectric transformation is unique in a way to estimate band-gap energy when there remain unresolved or multiple absorption peaks in the diffuse reflectance spectra. Importantly, the complex dielectric transformation method also distinguishes the class of the materials which is of paramount importance to validate and substantiate the band-gap energy values.