Accurate characterization of porous materials is essential for understanding material properties and evaluating their performance for potential applications. In general, any methodology that entails developing an accurate classical force field is computationally expensive as it requires a large number of quantum mechanical nonempirical calculations. In order to expedite such calculations without sacrificing too much accuracy, we have developed a systematic procedure where, starting from an initial trial force field, accurate adsorption isotherms of porous materials can be obtained at low computational cost. Specifically, the procedure involves correcting single-point energy values sampled from the trial force field in grand canonical Monte Carlo simulations from few quantum mechanical calculations. We demonstrate that the methodology yields accurate adsorption data in diverse selection of guest molecules in porous materials such as CH4 and CO2 in zeolites (i.e., MFI, LTA, WEI, RHO, SOD, FAU, RWY, and ABW) and CO2 in metal–organic frameworks (i.e., M-MOF-74 with M = Mg, Fe). Furthermore, we use our corrected force fields to predict the adsorption properties of N2 in V-MOF-74 and Ti-MOF-74, which are two materials that have yet to be synthesized experimentally. We anticipate that this methodology will be useful in accurately characterizing a given porous material in the absence of a reliable force field as well as for efficiently screening a large number of porous materials.