An electro-resistivity technique for measuring a proxy for froth bubble sizes as a function of height above the pulp-froth interface has been developed. Froth phase bubble size measurements were performed in a laboratory mini-flotation column. Comparison of the proxy herein termed average intra-bubble impact distance (LID) from this new technique to the Sauter-mean diameter from the conventional photographic method established a linear correlation. The average IID from the new technique was higher than the Sauter-mean diameter at all froth segments. Both techniques were able to capture the general increase in bubble sizes as a function of froth height. (C) 2014 Elsevier B.V. All rights reserved.