Nanofluids are considered for improving the heat exchange in forced convective flow. In literature, the benefit of nanofluids compared to the corresponding base fluid is represented by several figures-of-merit in which the heat transfer benefit and the cost of pumping the fluid are considered. These figures-of-merit do not account for the limited heat capacity of the fluid, the geometry and the flow conditions that in addition affect the temperature of the heat-transfer surface. We address these limitations by deriving a figure-of-merit that includes all the relevant thermophysical properties of the fluids, the flow conditions and the geometry of the heat-transfer device. This figure-of-merit is a useful benchmark tool to evaluate nanofluids in a laminar flow regime for heat sink applications. (C) 2013 Elsevier Ltd. All rights reserved.