Using computer-generated three-dimensional molecular models, we verify that the surface area of vitrinite from HvC bituminous coal depends on the size of the unit used to measure the surface (the adsorbate size), the size of the model (the particle size), and the micropore size distribution. By varying these three factors, we demonstrate that the surface area of our bituminous coal models is characterized by a single number (D = 2.71)-the fractal dimension. Our micropore size distribution, which is a consequence of the fractal dimension, reveals that most of the micropores are ultramicroporous (having an pore entrance size less than 0.8 nm).