Disclosed is a sizing device for sizing an inside diameter of a lung passageway. The device includes an elongate shaft configured for positioning in the lung passageway and a sizing element at the distal end of the shaft. The sizing element defines a range of transverse dimensions that correspond to a range of transverse dimensions suitable for use with a predetermined set of bronchial isolation devices. The device is used to determine the suitability of a bronchial isolation device for use in the lung passageway prior to using a separate delivery catheter to deliver the bronchial isolation device into the lung passageway.