Existence of high quality caprocks is one of the necessary conditions to realize effective geological sequestration of CO2. Existing measures for the evaluation of caprock sealing ability cannot represent the sealing effect of formation thickness. New quantitative measures for characterizing the sealing ability of caprock with pore networks were developed for CO₂ geological storage. The new measures, actually as a synthesis of numerous conventional and commonly used parameters, are related to the maximum pressure the caprock can sustain to prevent the CO₂ leak to the topmost position of the caprock. The measures are capable of reflecting the role that formation thicknesses play in addition to the traditional capillary sealing mechanism and the formation pressure sealing mechanism. It is also anticipated the new measures are applicable to evaluations of natural gas caprocks. Case study shows that the new measure usually predicts higher sealing ability than that by the traditional measure mainly due to the consideration of formation thickness.