A level gauge includes a housing, a vertical member, and a perpendicular member. The housing includes a bottom wall and a side wall. A surface of the side wall includes a first scale. The bottom wall and the side wall enclose a receiving cavity. The vertical member is arranged in the receiving cavity and includes an axis maintained in a vertical orientation in a natural state. A center of gravity of the perpendicular member is arranged on top of the vertical member. A plane of the perpendicular member is maintained perpendicular to the axis of the vertical member. When the bottom wall is placed on a gauging surface, an inclination angle and inclination direction of the gauging surface are obtained simultaneously.