A power storage system includes a power storage device configured to be charged and discharged, and a controller configured to calculate an open-circuit voltage of the power storage device from relationships between a plurality of current values and voltage values detected in a predetermined period during charge and discharge of the power storage device, specify an SOC corresponding to the calculated open-circuit voltage, from a correspondence relationship between the SOC and the open-circuit voltage of the power storage device, and calculate a full charge capacity of the power storage device, based on the SOC specified with respect to each of a first period and a second period during charge and discharge, and an integrated value of charge and discharge current of the power storage device from the first period to the second period. A method of calculating the full charge capacity in this manner is also provided.