This paper presents a simple iterative method for optimally sizing an inverter in a grid-connected photovoltaic (PV) system. Hourly solar radiation and ambient temperature data are used in this work for developing the models of grid-connected PV system. The results show that for the adapted case, the optimum inverter size ratio is 1.66 whereas the maximum efficiency reaches with this sizing ratio is 95.16%. Moreover, a comparison study is carried out between a conventionally sized inverter, with a capacity equals to the PV array capacity, and an optimized inverter. Based on that, the results show that the total energy produced from second case is higher than the first. Finally, the annual yield factor for optimum sizing system is higher than the conventionally sized system. This proves that the optimized PV inverter has better performance.