A low-cost experimental technique has been developed to screen the effectiveness of an adsorbent in improving the hydrogen storage capacity within a pressurized vessel. The capsule technique is shown to be effective in directly measuring the total H2 contained within a pressurized vessel and can be used to evaluate the amount of gas in the free space and adsorbed on the solid, i.e., a sorption isotherm. The capsule technique was benchmarked by measuring isotherm data for CH4 on an activated carbon sample and was then subsequently evaluated for use with H2. The capsule data are in excellent agreement with the total storage capacities expected from calculations using equation of state information. In addition, H2 isotherm data from the sorption capsule are found to be within 1% of values obtained from a more sophisticated differential pressure adsorption unit (DPAU). Conditions for when the adsorbent aids or hinders storage are also discussed.