Two hydrogen-uptake measurement methods are used for the characterization of MOFs as hydrogen storage materials: gravimetric and volumetric. To obtain the total amount of hydrogen in the MOF, both the amount of hydrogen absorbed on its surface and the amount of hydrogen residing in its pores should be considered. To calculate the absolute absorbed amount ("N"abs), the surface excess amount ("N"ex) is added to the product of the bulk density of hydrogen (ρbulk) and the pore volume of the MOF ("V"pore), as shown in the following equation: