A method to simulate the Resistive Plate Chambers (RPCs) γ sensitivity has been developed using a Monte Carlo code. The sensitivity has been evaluated as a function of the γ energy in the range 0.1–100 MeV and for different spectra. To evaluate the response of the detector in a Large Hadron Collider (LHC) background environment the γ energy spectrum expected in the CMS muon barrel has been taken into account and the RPC γ sensitivity evaluated as a function of the detector size.