A novel characteristic variable of fill level has been proposed, in order to reduce the influence of various factors on measuring the fill level and improve the measurement accuracy of the fill level. A relationship was developed between the fill level and the angular position of the maximum vibration point on the mill shell through theoretical calculation and on-site experiments. This relationship was studied theoretically with two assumptions. The vibration signals were then collected by an accelerometer mounted directly on the mill shell, and analyzed on the time domain to obtain the maximum vibration point on the mill shell, in order to study the correlation between the fill level and this angular position. Both the results of theoretical calculations and experiments show that the position of the maximum vibration point on the mill shell moves to a lower angular position as the fill level increases. Comparison of the traditional and the new characteristic variable of the fill level reveals that the characteristic variable proposed in this paper is more superior and stable. It shows potential for measuring the fill level more accurately. (C) 2009 Elsevier Ltd. All rights reserved.