The U.S. Army has investigated a variety of multifunctional designs in order to achieve system level mass and/or volume savings. One of the multifunctional devices developed is the multifunctional fuel cell (MFC)—a fuel cell which simultaneously provides a system with structural support and power generation. However, there are no established methods for measuring how well a particular design performs or its multifunctional advantage. The current paper presents a metric by which multifunctional fuel cell designs can be characterized. The mechanical aspect of the metric is based on the specific bending stiffness of the structural cell and is developed using Frostig’s high-order theory. The electrical component of the metric is based on the specific power density achieved by the structural cell. The structural systems considered here display multifunctional efficiencies ranging from 22% to 69%. The higher efficiency was obtained by optimizing the contact pressure at the gas diffusion layer (GDL) in a model cell design. The efficiencies obtained suggest the need for improved multifunctional designs in order to reach system level mass savings.