The solid/liquid interfacial energies of pure metals and metallic alloys are modelled in this paper. A simple model is offered for pure metals, showing that their solid/liquid interfacial energy (sigma) slightly increases with temperature. Sigma for metallic alloys is considered for the interface between solid and liquid solutions being in thermodynamic equilibrium, calculated by the CALPHAD method. The Butler equation is extended to find the equilibrium composition of the solid/liquid interfacial region and the solid/liquid interfacial energy at fixed temperatures. This method takes into account the segregation of low-interfacial energy components to the solid/liquid interfacial region. It is shown how the new method can be extended to multi-component alloys. The method is applied to calculate the solid/liquid interfacial energy of Al-rich solid solutions in equilibrium with eutectic liquid alloys of Al-Cu, Al-Ni, Al-Ag and Al-Ag-Cu systems. Good agreement was found with experimental values. For the Al-Ag-Cu system, the modelled value allows to select the more probable experimental value from the two contradicting experimental values published in the literature. The solid/liquid interfacial energy is calculated for the eutectic Ag-Cu system as function of liquidus composition (which determines both the equilibrium solidus composition and the equilibrium temperature). Finally it is claimed that using solely bulk thermodynamic data (melting enthalpy and molar volumes of pure components and molar excess Gibbs energies of equilibrium solid and liquid solutions) it is possible to provide meaningful values for the temperature and concentration dependence of solid/liquid interfacial energies of alloys. The method can be applied for simulation of solid/liquid phase transformation and also to solid/liquid equilibrium calculations of nano-alloys.