Hydrogen generator with fuel gauge

The invention is a hydrogen generator with a fuel gauge and a method of fuel gauging. The hydrogen generator includes a replaceable fuel unit, containing a hydrogen-containing material (fuel) that can release hydrogen gas when heated and whose thermal conductivity is related to a quantity of releasable hydrogen contained therein, and a fuel gauge including a heat source and a temperature sensor adjacent to the fuel unit and a controller for determining a fuel level value based on a measured temperature. The temperature is measured at a pre-established time after activating the heat source, and the measured temperature is compared to a predetermined relationship between the measured temperature and a releasable hydrogen content in the fuel at the pre-established time. An output signal is provided (e.g., to a visible display, an audible signal or a controller).