This research investigated the unstudied impact, in 416 cases of stone-induced hydronephrosis detected radiographically in 369 patients, of stone size on the stone’s location in the urinary tract and on the hydronephrosis grade. Most (62.5%) of the hydronephrosis cases were Grade 2; 17.1%, Grade 3; 10.6%, Grade 4; and 9.9%, Grade 1. The mean size of the stones reported in the renal pelvis, pelviureteric junction (PUJ), upper ureter (UU), midureter (MU), lower ureter (LU), and vesicoureteral junction (VUJ) that caused hydronephrosis were 23.03 ± 8.97 mm, 15.56 ± 6.59 mm, 12.91 ± 6.02 mm, 11.05 ± 4.27 mm, 10.41 ± 4.80 mm, and 6.73 ± 3.28 mm, respectively. The mean size of Grade 1-causing stones was 16.63 mm; Grade 2, 11.49 mm; Grade 3, 15.69 mm; and Grade 4, 21.23 mm. The mean stone size significantly decreased from the renal pelvis, through the PUJ, UU, MU, and LU, and down to the VUJ and increased as the hydronephrosis grade increased from Grade 2 to Grade 4. In conclusion, large-size stones were predominantly located in the renal pelvis and PUJ, with few located in the lower ureter, and no large stones reached the VUJ. Small-size stones were mostly located in the VUJ, with only one stone in the PUJ, and no small-size stones were present in the renal pelvis. Large-size stones caused severe hydronephrosis, and small-size stones caused grade 2 hydronephrosis. Increases in stone size decreased its passage rate in the ureter and increased the chance of causing high-grade hydronephrosis. These results alert urologists to adopt faster therapeutic procedures for larger stone sizes to reduce renal damage caused by obstructive uropathy.