A quasi-1D simulation model was developed to estimate total area-specific resistance for overvoltages (R-tot) and cell voltage by separating gas conversion impedance (GCI) from overall real-part impedance in high temperature steam electrolysis with a solid oxide cell (SOEC). GCI and R-tot for a square cell was estimated as 0.012-0.011 Omega cm(2) and 0.206-0.216 Omega cm(2), respectively, at J = 0.0-1.8 A cm(-2), 800 degrees C, and relatively high flow rates. Even though GCI is small compared to R-tot, ignoring the GCI will result in higher simulation errors at J > 0.5 A cm(-2). Simulation results attained +/- 0.3% or better precision against measured cell voltages at 750-850 degrees C. Furthermore, case studies at 800 degrees C revealed +/- 40% local current density distribution in the cell at 1.0 A cm(-2) and 82% steam utilization. GCI was roughly inversely proportional to gas flow-rates and depended on steam utilization. Improvement of R-tot to 0.150 Omega cm(2) could attain more than 1.75 A cm(-2) at 1.30 V. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.