Based　on　FEM　calculations,　a　simple　polynomial　expression　for　surface　strains　of　cone　indented　elastic　plastic　solid　was　obtained　using　regression　method,　which　facilitated　an　engineering　solution　for　interfacial　toughness　of　thin　ceramic　coatings　on　metallic　substrates　using　just　a　standard　Rockwell　hardness　test.　Testification　was　made　on　a　TiSiCN　coating　of　steel　substrate　with　a　50　nm　thickness　Ti　interlayer　to　improve　adhesion,　and　a　reasonable　value　of　the　interfacial　toughness　of　205　J/m(2)　was　gained.　(C)　2008　Published　by　Elsevier　Ltd.　on　behalf　of　Acta　Materialia　Inc.