The conditions for which free convection and forced convection in the thin laminar boundary layer regime produce the same Nusselt number are indentified and generalized. Such conditions are herein designated as equivalents, and the relationship between the two conditions is designated as an equivalence. The concept of equivalence provides a new structure for the assembly of information on heat transfer and mass transfer, and therefore, a new resource for teachers as well as for practitioners of transport and process design. It is the commonality of the equivalence for different conditions and geometries that renders it uniquely useful in these regards.