This paper presents a method for upscaling permeability of fractured coal using the cubic law to quantify permeability of the fracture system. The version of the cubic law that incorporates the length/tortuosity effect available in the literature was modified by including a connectivity parameter. All parameters of the modified cubic law (fracture aperture, porosity, length, and connectivity) were estimated for a set of coal samples using quantitative methods available in the literature. The geometry of the fracture system within the coal samples was determined from micro computed tomography scans. Parameters of the modified cubic law estimated from the scans were validated by comparison of the resulting permeability to the numerical simulation of single-phase fluid flow in fractures, which was developed at the previous stage of this study. The modified cubic law was then used for upscaling of permeability from the millimeter scale to the centimeter scale. It produced the results that match the literature data for the coal from the same region as well as the experimental data for the studied area.