In this study, a 1‐D electrochemical model was employed to predict the effect of key design parameters, such as carbon‐to‐sulfur (C/S) ratio, electrolyte‐to‐sulfur (E/S) ratio, and sulfur loading on the discharge capacity and voltage profile of a lithium‐sulfur (Li−S) battery. Herein, a novel definition for the electrochemically active area is proposed based on the weight fraction of carbon and a reference porosity in the cathode. The experimental trends of the discharge behavior of a Li−S cell were captured by the model regarding the change in key design parameters. Results were given in comparison with the predictions of two other models that use different active area definitions, and it was concluded that a sensible representation of the electrochemically active area is critical for modeling the effect of cell design on the discharge performance of a Li−S battery.