Abstract: Apparatus and method for determining the filling level of a liquid in a container is provided. The apparatus includes at least one element coupled with a body at least partially immersed in the liquid, the at least one element transmitting and/or receiving acoustic signals. The at least one element may include an element that both transmits and receives acoustic signals, and may include elements that have a transmitting-only element and a receiving-only element. The acoustic signals generated by the at least one element propagate along a surface of the body, which may be solid or hollow. The body is arranged in such a manner that at least one part of a surface can be wetted by the liquid. The body has, at different container heights, regions which reflect the acoustic signals that may be detected and analyzed by a unit to determine the container liquid level.