In this paper, we present a water volume estimation method in various cups using the glass harp acoustics. When a rigid probe flicks a glass, sounds arise. Since the sounds alter depending on the water volume in the glass, we can utilize the sound information to estimate the water volume. In order to model the acoustics characteristics of various glasses, we propose the relational expression between the water volume and the vibration frequency that improves Oku's expression. By using the proposed relational expressions and a flicking motion by a robotic finger with a microphone, we confirm the proposed method can estimate the water volume with the accuracy of 1–3%.