In this research, a parametric study was conducted on effects of using the ACI and BS codes on the amount of required longitudinal and transverse reinforcement to resist different load combinations applied to rectangular RC beams. The design results were judged based on required amount of longitudinal and transverse reinforcements. In the case of combined bending moment and shear force, it was found that both codes required almost same flexural reinforcement with maximum difference of 3.7% for M u/V u = 2. However, the results differ largely on the transverse reinforcement with the change of M u/V u ratio. The differences become pronounce with the increase of M u/V u ratio leading to continually diverging curves with 26.2% difference for M u/V u = 2. In most cases, it was found that the BS requires less reinforcement than the ACI. In the case of pure torsion, it was found that the required longitudinal and transverse reinforcements by ACI were larger by 19.2% and 19% than the BS respectively.