Many researchers have been interested in finding elements that help in calculating the orbital angular momentum (OAM) of perturbed vortex beams i.e., after propagating through turbulence in recent years. In this work, we realized a method that utilizes the area of spatial auto-correlation function of scattered optical vortices for finding the topological charge. We have also established an analogy between the area of the intensity auto-correlation profile of the partially coherent vortices and the radii of the related coherent ring-shaped vortex beam transverse profiles which helps us finding the topological charge in a simpler way. This method is independent of the beam waist of Gaussian laser beam for generating the vortex beams. Our experimental results are in good agreement with the theoretically obtained results. These results may find applications in free space optical communication and ghost imaging with vortex beams.