Froth depth is currently measured in industrial flotation columns using a float coupled to an ultrasonic sensor, and less frequently using pressure transducers. The use of the conductivity profile in the upper part of the column has been proposed by some researchers but never used in plants on a regular basis. As compared to traditional ones, this method has the advantage of providing information that could also lead to the evaluation of other internal variables such as the bias rate. In this work, an exhaustive revision of the conductivity-based methods and the most important improvements recently introduced, are presented. Particularly, a novel approach based on a weighted average interpolation is presented, which greatly improves the precision and the smoothness of the estimations. (C) 2008 Elsevier Ltd. All rights reserved.