This paper presents a study of the effect of back pressure variation on the mass flow rate and normal shock occurrence in a sonic nozzle. ANSYS-FLUENT software was used for numerical simulation, and experimental measurements were carried out to verify the numerical results. Nozzles of various designs (different divergence angles and throat diameters) were subjected to investigation. The simulation results indicate that both the divergence angle and the throat diameter markedly influence the performance via the occurrence of normal shock in the divergent part of the nozzle. The nozzle throat diameter ranges from 0.558 to 3.175 mm, and the back-pressure ratio is 0.6. Normal shocks move toward the nozzle exit upon a decrease in divergence angle and an increase in throat diameter. For this diameter range, the corresponding distance from the nozzle inlet toward the divergent section at which a normal shock occurs is 2.8 to 3.2.