The problem of determining nonlinear-optical characteristics of working substances of limiters of high-power laser radiation is analyzed. A new method of simultaneous calculation of the beam-waist radius and nonlinear absorption coefficient from the Z-scan data is proposed. The value of nonlinear optical characteristics of ZnSe, porphyrin-graphene (Graphene-TPP), fullerene-graphene (Graphene-60), polyethylene oxide containing multilayer carbon nanotubes (PEO/MWNT), along with polymethine dyes PD-792 and PD-7098 and dicyanomethylene-pyran dyes DCM-627 and DCM-684, are obtained. Different working substances are compared for the first time under the same conditions by plotting output characteristics of laser-radiation limiters. The change of the laser-pulse shape after propagation through the limiters with different working substances is demonstrated.