Various mechanisms and correlations have been developed for prediction of thermal conductivity of nanofluids. In this work, a simple equation has been proposed for prediction of thermal conductivity of all suspensions, including suspensions containing microparticles and nanoparticles. This equation relates thermal conductivity of suspensions to the mean distance between the particles. For ordinary suspensions - suspensions containing micro- or millimeter sized particles - this distance can be equated to the effective diameter; however, for nanofluids, the Brownian motion approach should be used to estimate it. Nevertheless, since all required assumptions for deriving Brownian motion relations do not hold for nanofluids, we assumed this distance can be evaluated using an adjustable coefficient multiplying the mean free path - or distance between particles - calculated by Brownian motion approach. The applicability of the proposed model has been proven by comparing the results with our experimental data. (C) 2010 Elsevier B.V. All rights reserved.