Real time ellipsometry has been used to measure critical nucleation parameters, such as the incubation time, nuclei growth rate and nuclei density. Typically, the nuclei geometry is unknown. Therefore, quantitative analysis of real time ellipsometric data is dubious due to the inadequacy of the optical model. In this article we report a novel technique based on a square relationship that exists between nuclei height and volume fraction for a variety of nuclei models. This relationship enables quantitative analysis of real time ellipsometric data for thin film nucleation and growth without a knowledge of the exact nuclei geometry,