This paper introduces a numerical method of reconstructing three-dimensional (3D) ultrasound fields from their two-dimensional back-projections to understand the intensity distribution of nonplanar waves. The horizontal planes for line-focused ultrasound fields were roughly elliptical, whereas those for point-focused ultrasound fields were nearly circular. Experimental and simulated results indicated that the ultrasound intensity at the central axis can be calibrated from the light intensity by 3D reconstruction of the ultrasound field. The difference between the measured ultrasound intensity for nonplanar waves in schlieren imaging and the simulation results were discussed. From this work, the 3D ultrasound field becomes possible to be reconstructed.