Performance parameters and relationships typically reported about the electrodes in an electrochemical capacitor generally do not allow active material value to be determined. This is primarily due to non-ideal dynamical behavior of these storage materials, which typically is a result of having high surface area. We show that electrochemical capacitor active material value can be quantified using a derived equivalent circuit model in combination with circuit simulations. The circuit model embodies electrical characteristics of the active material in device form and SPICE simulations allow model validation and storage system design, which is necessary to establish active material value. We demonstrate this approach starting with test data from a small activated-carbon, aqueous-electrolyte capacitor and proceed to design a regenerative braking-energy storage system for a 20-ton city transit bus. A value is then assigned to the active material in the capacitor based on its functional performance. For a specific energy storage application, this approach can provide value quantification of various active materials and thus allow for legitimate comparisons. (C) The Author(s) 2017. Published by ECS. All rights reserved.