A general correlation is proposed for the laminar Graetz problem associated with convection in ducts of arbitrary cross-section. The correlation assumes knowledge of fully developed transport constants, specifically the product of fully developed friction factor and Reynolds number, and the fully developed value of Nusselt number, whose values are particular to the duct geometry and wall condition. The new correlation is suitable for ducts having a convective surface equal to the wetted perimeter, and for ducts having a wall condition of either constant temperature or constant heat flux. For the majority of solutions to the Graetz problem found in the literature for various duct geometries, the new correlation is generally found to be within +/- 5% of first principle calculations. (C) 2019 Elsevier Ltd. All rights reserved.