Hydrogen peroxide or H2O2 has been widely used as a green propellant in various types of thrusters based on catalytic decomposition. However, no standardized design methods for H2O2 catalyst beds exist at present. In this study, we scaled a catalyst bed for a H2O2 monopropellant thruster using catalytic decomposition modeling. We adopted the model developed by Pasini et al. (2010)  to simulate the catalytic decomposition of H2O2 in the catalyst bed. The one-dimensional profiles of temperature, pressure, species concentration, and other properties were estimated using the model. Additionally, static firing tests were conducted under various conditions using a 100-N H2O2 monopropellant thruster with a MnO2/PbO/Al2O3 catalyst. The simulation results were compared with those obtained from the static firing tests to validate the accuracy of the model. We observed that the temperature estimations from the model concurred with those of the experimental data; however, pressure estimations deviated slightly. Furthermore, the model was used to obtain the design parameters for scaling based on catalyst capacity and pressure drop analyses under various conditions. We determined that the pressure drop can be scaled and expressed as a constant. Thus, the catalyst bed can be scaled precisely by analyzing the catalyst capacity and pressure drop constants through catalytic decomposition modeling.