A proper quantification of the specific surface area of nanoporous materials is necessary for a better understanding of the properties that are affected by the high surface-area-to-volume ratio of nanoporous metals, nanoporous polymers and nanoporous ceramics. In this paper we derive an analytical expression that relates the specific surface area of arbitrary nanoporous materials to their solid bulk density and ligament size. Computed specific surface areas of porous materials with regular nanopores are in good agreement with the expression derived. These regular void geometries include single and double gyroid structures, as well as materials with spherical and cylindrical nanopores. Validation of the expression for disordered nanoporous materials is performed by investigation of the specific surface areas of various nanoporous gold electrodes in the double-layer charging regime. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.