Three dimensional (3D) modelling of supercapacitors (SCs) has been investigated for the first time to have a better understanding of and study the effect of each parameter on the final electrochemical results. Based on this model, the resistance of the electrolyte, membrane, current collectors and active materials have effects on the first intersection points on the real axis (x-axis) of the Nyquist plots (equivalent series resistance (ESR)). These results indicate inward shrinking of the cyclic voltammograms (CV) due to a small change in the leakage resistance and resistance of the faradic component of materials, and they also explain the parameters that lead to the deformation of the CV from ideal behaviour. The 3D model was verified with experiments using activated carbon-based SC devices. The experimental results confirmed the 3D model results and suggested that the proposed 3D model is reliable and can be used for the proper design of SC devices.