A catalyst withdrawal apparatus and method for regulating catalyst inventory in a fluid catalytic cracking catalyst (FCC) unit is provided. In one embodiment, a catalyst withdrawal apparatus for removing catalyst from a FCC unit includes a pressure vessel having a metering device coupled to a fill port. A heat dissipater is located adjacent the metering device and is adapted to cool catalyst entering the pressure vessel. A sensor is coupled to the pressure vessel arranged to provide a metric indicative of catalyst entering the pressure vessel through the metering device. In another embodiment, a method for regulating catalyst inventory in a FCC unit includes the steps of determining a change of catalyst present in a FCC unit, withdrawing catalyst from the FCC unit into an isolatable storage vessel coupled to the FCC unit, measuring the amount of catalyst disposed in the storage vessel, and removing the measured catalyst from the storage vessel.