The degree of paraxiality is one of the important parameters to characterize beam propagation. It shows the difference between the real beam and some reference beam that is the same beam without divergence. Such a beam is nonphysical and we propose to expand the beam propagation into the full space and use the point source as a reference beam.Propagation of nonparaxial beams has been extensively investigated by different methods but the standard approach is substitution of known or assumed field distribution or its Fourier spectrum in some plane into one of diffraction integrals [1][2][3][4][5]. To simplify calculations these integrals are often replaced by their paraxial analogues. Accuracy of results substantially depends on the difference between propagation of the real beam and some reference beam which propagation is exactly predicted by used paraxial approximation of diffraction integral. To characterize such an error quantitatively two new parameters has been recently introduced: the paraxial estimator C PE [3] and the degree of paraxiality C [4]. Both parameters are the ratio of the total power and integrated intensity. In both of them only the field distribution in the initial plane is used but in C PE this distribution is the cross-section of the solution of paraxial wave equation whereas in C its origin doesn't matter. The importance of the parameter that characterizes paraxiality is obvious because the calculation error itself may be negligible but to estimate reliability of results the level of approximation error must be known and acceptable. Note, then the ratio C is also known as radiation efficiency and has been used to characterize the difference between partially and fully coherent beams [6]. ( ) ( ) ∫ ∫ ∫ ∫ ∞ ∞ = = 0 2 0 2 0 2 0 0 0 , , dr r r U d dr r r S d