Recently a number of industrial scale pulsed disc and doughnut (PDD) solvent extraction columns have been operating with no pulsation. However most of the published research studies in the literature that describe and predict the performance of PDD columns were developed for pulsing conditions. In this study the Sauter-mean drop diameter, d(32), was measured and correlated under pulsing and non-pulsing conditions using a 75 mm diameter PDD column. Under non-pulsing conditions, the results show that the d(32) slightly decreased with increasing dispersed phase velocity, while there was no noticeable change in d(32) with continuous phase velocity. Under pulsing conditions, the d(32) decreased with increasing pulsation intensity from zero. The cumulative drop size distribution in disc and doughnut columns was found to be predicted well using the Weibull function. A new unified correlation was proposed in this study to predict the experimental d(32) data of the PDD column used in this study, as well as published experimental data which was obtained using different systems and column geometries, over a wide range of pulsation rates including no pulsation. (C) 2016 The Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.