Gas-liquid porometry is a common method for characterizing microfiltration (MF) membranes. This paper provides a modified approach to analyze data from it. Herein, we combine porometry results with porosity measurements to improve prediction of the gas and liquid permeances through the membranes. Pore size distribution (PSD) and porosity measurements were performed for a range of membranes including symmetric and asymmetrically-stacked symmetric membranes, and an intrinsically asymmetric membrane. Our modified approach determines the tortuosity for each pore size bin (range) during the estimation of the PSD. For the symmetric MF membranes, there was high discrepancy between the measured mean pore size and the manufacturer's data, thus, reinforcing the importance of knowing the basis for membrane ratings. Our study also examined the effect of asymmetry on the measured PSD. The asymmetric membranes were found to give a smaller mean pore size compared to their symmetric component membranes. Additionally, the orientation of asymmetric membranes provided different results for both the mean pore size and tortuosity. A comparison between the common and modified approaches to analyze the data was made through the estimation of liquid permeances. Better correlation (at least a 7% improvement) of measured and estimated permeances for several fluids was found for our modified approach as compared to the classical methods because of the inclusion of a specific tortuosity for each pore size bin. The average tortuosity of the membranes under study varied from 0.936 to 5.020 with the larger nominal pore membranes having higher values compared to the smaller ones. (C) 2012 Elsevier B.V. All rights reserved.