A device for calculating a quantity of fuel in a fuel tank for a fuel cell vehicle is provided. The device includes a first quantity determining system that provides a first quantity value representing said quantity of fuel in said fuel tank based on a physical condition associated with said fuel in said fuel tank, a second quantity determining system that provides a second quantity value representing said quantity of fuel in said fuel tank, and an error correction system that generates an error value based upon the first quantity value and the second quantity value. A method for calculating a quantity of fuel in a fuel tank for a fuel cell vehicle is also disclosed.