[en] The dark mass problem is the most important for cosmology and galaxies physics. Various observational data of galaxies and galaxies clusters kinematics and dynamics require presence of massive dark matter. We estimate the dark mass within the galaxies optical radius using several different approaches, such as the maximum disk model, the marginal condition of the stellar disk gravitational stability and the vertical equilibrium condition in the galactic disk. The distribution functions of the relative dark mass within the optical radius R_opt for a set of 50 galaxies are constructed. Most of the objects from our set have a relative mass within µ = 2. This agrees well with the results of numerical simulations. (paper)