One of the main problems related to Rockwell hardness measurements is the influence of the indenter shape. In the present work the effects of the macro-geometry of the diamond indenter are analyzed as influencing parameters in Rockwell C test. Both an experimental analysis is carried out, using IMGC National Standard Machine, and a finite element simulation (FEM) is performed. Four different theoretical models are proposed to interpret experimental results: the first model is based on Brinell definition of hardness, the second on Meyer analysis and the last two are based on the evaluation of the deformation work through the analysis of the indentation volume. These different corrections are compared to evaluate their performances.