In this paper, we propose an empirical formula for i(0,TPB), the exchange current density per unit triple phase boundary (TPB) length, for porous lanthanum strontium manganite (LSM) cathodes of solid oxide fuel cells (SOFCs); the evaluation of i(0,TPB) is of crucial importance in numerical simulations of electrodes based on reconstructed microstructures obtained by a dual beam focused ion beam scanning electron microscopy (FIB-SEM) and tomography techniques. To derive a widely applicable empirical formula for i(0,TPB), electrochemical measurements of porous LSM cathodes are conducted under various oxygen partial pressures (0.05-0.25 atm) and temperatures (800-950 degrees C). By comparing the derived formula with that derived from a thin and dense patterned LSM electrode used in previous studies, it is found that at an air temperature of 800 degrees C, imTs derived from a porous LSM cathode is approximately 40% smaller than that for the patterned electrode. This can be attributed to the fact that the electrochemical reaction in thin and dense electrodes can occur not only at the TPBs but also at the LSM surface owing to the non-negligible ionic conductivity of LSM. The derived formula is also applied to a three-dimensional numerical simulation to confirm its validity. (C) 2016 Elsevier B.V. All rights reserved.