The complex structure of activated carbon can be described as a three-dimensional network of graphene layers oriented in random directions. In this work, we propose a new model of the microporous structure, taking into account the degree of activation. We derive a structural relation between porosity, skeletal density, specific surface area, and the number of graphitic blocks per unit volume. In addition, we present a new approach to evaluate the interdependency between porosity and specific surface area by combining high-resolution scanning transmission electron microscopy and subcritical nitrogen adsorption. Finally, we propose a structural metric that predicts the relation between the volumetric storage capacity and the gravimetric storage capacity of supercritical methane at room temperature.