Compared to satellites and balloon-borne experiments, ground based air shower detectors enjoy larger fields-of-view and higher effective areas, making them ideal for studies of gamma rays above TeV energies. The Gamma Ray Astronomy at PeV EnergieS Phase-3 (GRAPES-3) experiment is an extensive air shower (EAS) array located in Ooty, India, with $\sim$400 densely packed scintillator detectors accompanied by a 560 m$^2$ muon telescope. With the recent improvement in the angular resolution and an effective background rejection efficiency, the GRAPES-3 experiment has an excellent ability to study gamma-ray sources in the ultra-high energy (UHE) regime. In this work, we will present the acceptance of the GRAPES-3 towards gamma-ray-initiated showers, studied using CORSIKA simulated data.