The capacity and power consumption dependences on the pressure drop are necessary for selecting single-screw pumps (SSP). Most manufacturers publish publicly available dependencies of the SSP specified characteristics on the rotor speed. The article develops a method for constructing load characteristics based on test results. An analysis of the test results showed the need to take into account the minimum speed of rotation, at which the liquid begins to pump. This frequency increases markedly with the increasing pressure drop. The proposed method allows to determine the values of characteristics at idle that are not present in the test results with a high degree of confidence. For example, the characteristics of the pump SP-76-02 are considered. The values of the optimal pressure drop efficiency at acceptable frequencies are in the operating range (below 1.2 MPa). The maximum efficiency is 77.2 % at a pressure drop of 1.2 MPa and a frequency of 600 rpm. The extreme mode goes beyond the operating range at a frequency above 200 rpm.