Quantification of interface properties such as two phase boundary area and triple phase boundary length is important in the characterization of many material microstructures. in particular for solid oxide fuel cell electrodes. Three-dimensional images of these microstructures can be obtained by tomography schemes such as focused ion beam serial sectioning or micro-computed tomography. We present a high accuracy method of calculating two phase surface areas and triple phase length of triple phase systems from sub-voxel accuracy segmentations of constituent phases. The method performs a three phase polygonization of the interface boundaries which results in a non-manifold mesh of connected faces. We show how the triple phase boundaries can be extracted as connected curve loops without branches. The accuracy of the method is analyzed by calculations on geometrical primitives. (C) 2010 Elsevier B.V. All rights reserved.