The melting behavior of nanometer-sized Sn particles with radius in the range between 5 and 50 nm is analyzed within the conceptual framework of classical thermodynamics. Experimentally observed size-dependent melting points and latent heats of fusion are exploited to point out the occurrence of pre-melting phenomena at the particle surface. The size-dependent values of the thermodynamic state functions associated with the solid-liquid interface are estimated together with the thickness of the interface layer.