Radius　and　area　function　of　a　spherical　indenter　are　calibrated　by　performing　spherical　nanoindentation　tests　on　fused　silica　with　known　properties.　The　spherical　indenter　is　made　of　ruby　with　a　relatively　large　radius　of　200　μm　in　nominal　value.　Hertzian　relation　was　found　to　be　successful　in　characterizing　radius　of　spherical　indenter　under　purely　elastic　deformation　condition.　Oliver　and　Pharr＇s　method　is　dependent　on　the　measurement　accuracy　of　residual　displacement,　which　cannot　be　measured　within　acceptable　precision　under　very　little　plastic　deformation　with　values　of　residual　displacement　being　only　several　nanometers.　Area　function　calibrated　with　Oliver　and　Pharr＇s　method　on　a　brittle　material　like　fused　silica　was　found　to　be　smaller　than　true　value,　leading　to　measured　elastic　modulus　larger　than　true　value.　A　softer　material　that　can　produce　sufficient　plastic　deformation　with　large　residual　displacement　is　recommended　as　the　standard　material　for　area　function　calibration.　©　2018　Elsevier　Ltd