A generalized correlation for combined entry convection in ducts of arbitrary cross-section has been developed. The correlation is constructed for the average Nusselt number using knowledge of fully-developed transport constants. The general correlation reproduces first principle solutions for the well-established round and parallel plate duct geometries to within ±5% for both constant temperature and constant heat flux wall conditions when Pr=0.7. A survey of the literature demonstrates that the new generalized correlation performs as well or better than existing correlations that are limited to specific geometries and wall conditions. The new correlation is generally in good agreement with first principle solutions of less common duct geometries so long as the duct has a convective surface equal to the wetted perimeter. The new correlation is not recommended for ducts having small aspect ratios that pinch the flow when convection is prescribed by the H2 constant heat flux wall condition.