Different weighting functions for calculating the specific surface area and average bubble diameter in froth flotation have been studied. The weighting functions considered were number length, area and volume. Using bubble size distribution data obtained from image processing of batch flotation froth, specific surface area and average equivalent diameter were calculated. It was found that weighting by surface area was the most appropriate method to determine both specific surface area and average equivalent diameter. The equivalent ellipsoidal diameter was found to be a more appropriate average diameter than the equivalent spherical diameter. (C) 2000 Elsevier Science Ltd. All rights reserved.