In this paper, a new methodology to extract the plastic properties of metallic materials from an instrumented spherical indentation loading curve has been proposed using dimensional analysis and finite element computation. The representative strain ε_r as defined in [Acta Mater 49 (2001) 3899] for sharp indentation has been extended to spherical indentation, and identified as the function of the indentation depth h with respect to indenter radius R. The representative strain has been used to determine the closed-form expression of the indentation load at various given indentation depths, which is a function of the representative stresses and reduced Young's modulus. Based on the analytical results reported in this paper, an inverse approach has been presented which allows the plastic properties of metal materials to be determined using the spherical indentation loading curve. The properties of the present inverse problem, i.e. the existence, uniqueness and stability of the solution, have also been investigated to identify the extent to which the present method can be applied effectively.