Single-component permeation is accurately measured for helium, nitrogen, argon, and oxygen through a pellet of commercially available activated carbon using the traditional time lag permeation technique. At low pressures (<10 Torr) Knudsen diffusion is found to dominate the diffusion process. At higher pressures where transitional slip and viscous flow is occurring, the flow rate is found to be highly dependent upon the pressure. The relationship between pressure and the measured flow rate for this experiment is determined and subsequently used to characterize the porous media.