Nematic liquid crystals (NLCs) have proved to be good surrounding materials to investigate variations of physical properties produced by plasmonic resonance in metallic nanoparticles (NPs). In this framework, availability of a simple and reliable tool enabling a complete analysis of dispersion in wavelength and temperature of the refractive index of a NLC containing NPs has been developed, which could reveal of great utility. By using the Extended Cauchy equations system applied to a particular NLC (E7), we have here implemented a simple formula that yields a fine evaluation of the NLC refractive indices dispersion in the wavelength range [450, 656] nm and in the temperature range [15, 55]degrees C. This allow also to estimate with quite high accuracy temperature variations around the metal NPs produced by the plasmonic resonance.