The purpose of this study is to evaluate the efficacy of different focus sizes used in shock wave lithotripsy (SWL) in breaking up renal stones. Methods One hundred patients with radio-opaque renal stones up to 20 mm were included in this prospective trial from the urology department at Benha University Hospital. Patients were divided into two groups at random. Group A was overseen by F1 and Group B by F2.KUB determined the percentage of patients who were stone-free after two weeks. There were no statistically significant differences between groups with respect to loin pain (P = 0.121), loin pain duration (P = 0.963), stone size (P = 0.443), stone density (P = 0.6), stone number (P = 0.897), stone location, or hydronephrosis (P = 1.01).Stones were most often found in the left lower calyx (28%) of patients in group A, and the left mid-calyx (38% of patients in group B). Two-week residual (P = 0.024), residual size (P = 0.049), and stone-free rate (P = 0.033) all differed significantly across the groups. In terms of adverse effects, group B had a substantially greater incidence of both colic (22% vs. 10%, P = 0.027) and fever (20% vs. 6%, P = 0.034). In terms of hematuria, no significant changes were found (P = 0.239). A high stone-free rate can be achieved with a small focus size and a constant force and rate in SWL, but these findings need to be validated in the presence of other variables, such as breathing or stone movement, which can influence effectiveness.