Finding a combination of design variables for an optimized design target is the main aspect in fuel cell system design. Beside that, it has to be ensured that all requirements, on component and vehicle level, are met. Using a visualization approach, called Design Requirement Map, as a graphical presentation of the design target and the requirements of two degrees of freedom, helps to answer certain design questions and enable an estimation of the influence of requirements and operating points on the optimal system design. In this paper, first, the general fuel cell system design problem is formulated and, second, the Design Requirement Map is used to study the influence of requirements on the optimal combination of humidifier scale and air compression ratio. Designs with too small or too large humidifiers reveal as designs, which are constrained by at least one of the considered requirements. In addition, the influence for a multi-objective design target and different ambient temperatures and pressures are addressed. For certain design questions using Design Requirement Maps can be very helpful to evaluate the impact of requirements on the system design especially when considering different operating points. © 2021 The Authors. Fuel Cells published by Wiley-VCH GmbH