In this video we show the process of gas adsorption during the measurement of gas adsorption / desorption isotherms. We present the process of adsorption as the isotherm is collected, showing regions of the isotherm that relate to micro-pores, meso-pores and macro-pores, as well as the BET surface area. Finally, we show the derivation of micro-pore size data using DFT and meso-pore / macro-pore data using BJH methods.