Analytical relations for cross sections and efficiency factors of the extinction, scattering, and absorption are obtained within the framework of the method of physical optics for a round plate when the normal to its base coincides with the direction of incident wave propagation. It is shown based on the energy relationships relating the sought characteristics that the error in the method of physical optics is estimated by a linear combination of two integrals whose values depend only on the diffraction parameter p= ka (a is the radius of a plate). Different numerical estimates of the relationship of the method uncertainty with the diffraction parameter are presented.