In this study, the cooling of a gas turbine (GT) blade leading edge using a single row of five impinging air jets was numerically and experimentally investigated. The inner surface of the blade leading edge was depicted as a semicircle profile. The numerical study was performed using a shear stress transport (SST) turbulence model. On the other side, the experimental work was conducted using the infrared (IR) thermal camera. Additionally, the heat transfer characteristics were investigated with changing the Reynolds number () from 5000 to 40,000. The study was carried out for different cases based on the jet diameter (), named as fixed diameter (FD) and variable jet diameter in the streamwise flow direction, i.e., ascending diameter (AD) and descending diameter (DD). The local and average Nusselt numbers and heat transfer uniformity were studied at different operating and design parameters. The results revealed that for FD, increasing the jet diameter decreased the average Nusselt number while it enhanced the heat transfer uniformity. Furthermore, for all values of , the thermal performance of the AD was better than the DD, which has the worst heat transfer uniformity. Finally, predicted developed correlations to estimate the average Nusselt number, surface heat transfer uniformity, and performance evaluation factor (PEF) for all cases of jet diameter were introduced.