Using free-energy calculations on small crystalline clusters, we estimate the free-energy density gamma(SL) for the solid-liquid equimolar interface of a system of hard-sphere colloids. By studying the behavior of a crystallite at coexistence, we determine the dependence of gamma(SL) on the radius of curvature of the interface. An extrapolation to infinite radius of curvature (flat interface), yields gamma(SL)(R-->infinity)=0.616(3), in good agreement with recent numerical estimates. Subsequently, we consider the dependence of the interfacial free-energy density on the degree of supersaturation. Our simulations suggest that the gamma(SL) associated with the equimolar surface is fairly insensitive to changes in supersaturation. (C) 2003 American Institute of Physics.