Abstract: A rotating detonation engine (RDE) injector and method of creating the same. In some embodiments, the RDE injector is configured such that the fuel to oxidizer pressure ratio is in a range of 0.8775 to 1.4917. In some embodiments of the method of creating a RDE a particular combination of propellants is identified, and their gas specific constant and specific heat ratio are recorded. A plurality of initial flow conditions is established, and the compressible mass flow equation is used to determine an appropriate cross-sectional area of each injector to produce a fuel to oxidizer pressure ratio is in a range of 0.8775 to 1.4917.