Raman scattering spectroscopy is powerful, express and non-destructive method for control of phase composition of different materials. To determine the crystalline part, one should know the ratio of Raman cross sections of crystalline to amorphous phases. In this Letter we report on accurate comparative measurements of the Raman scattering from monocrystalline and nanocrystalline Ge, as well as from amorphous Ge films. Being accompanied by the respective optical transmittance/reflectance measurements, these data allowed us to estimate the integrated Raman scattering cross section ratios of monocrystalline and nanocrystalline Ge to amorphous Ge, for the first time. For monocrystalline Ge the obtained ratio is equal to 4, while for nanocrystalline Ge this ratio decreased monotonously with a decrease of the nanocrystal sizes. Some physical reasons of the experimentally observed dependence are proposed.