Molecular dynamics and molecular statics calculations have been performed to evaluate the formation energy of self-interstitial atom (SIA) clusters in -SiC. For SIA-clusters with stoichiometric composition, an attempt has been made to fit the calculated data points to a polynomial function of cluster size n. The resultant equation EF=1.01n1+2.04n1/2 may indicate the applicability to a wide range of cluster sizes. This formalization will be useful for the development of accurate model on nucleation and growth of SIA-clusters, which is required for the modeling on irradiation-induced microstructural evolutions of materials in nuclear fusion reactors.