Size　effect　of　the　nickel-based　single　crystal　superalloy　DD6　is　investigated　in　this　study　by　performing　nanoindentation　experiments　and　finite　element　(FE)　simulations　by　emphasizing　the　strain　rate　effect.　An　analytical　method　is　proposed　to　identify　whether　a　material　has　the　indentation　size　effect　(ISE)　based　on　incremental　formulations　of　the　indentation　strain　rate.　By　taking　ISE　as　a　critical　factor,　the　contact　area　is　further　described　by　considering　the　curvature　radius　of　non-ideal　indenters　due　to　wear　issues　in　practice.　In　order　to　emphasize　the　strain　rate　effect　during　indentations,　the　material　parameters　dominating　mechanical　properties　are　adopted　from　the　strain　rate　dependent　Johnson–Cook　model,　particular　for　the　nickel-based　single　crystal　superalloy.　Consequently,　the　dimensional　ISE　analysis　is　performed　by　proposing　a　theoretical　framework　to　establish　the　relationship　among　the　indentation　strain　rate,　the　indenter　tip　curvature　radius　and　the　applied　load–penetration　depth　(P–h)　curve　for　characterizing　nanoindentation　responses.　By　identifying　the　indenter　curvature　radii　and　loading　time　as　the　important　external　factors　of　hardness　measurement,　FE　simulations　are　validated　to　achieve　good　agreement　with　experimental　data.　The　validated　FE　predictions　are　reliably　employed　to　calibrate　the　dimensionless　model　of　hardness　with　different　indenter　curvature　radii　and　loading　rates.　In　the　proposed　form　of　the　dimensional　hardness　model,　it　is　found　that　the　indenter　curvature　radius　can　be　perfectly　independent　of　the　material　constitutive　properties　and　loading　rates.　It　reveals　the　potential　and　advantageous　determination　of　characteristic　length　of　materials　by　using　nanoindentation.　©　2024　The　Authors