Although hardness testing is a cost-effective and reliable technique to quickly estimate the overall mechanical properties of materials, hardness is not a fundamental mechanical parameter and it is rarely used in constitutive modeling or in engineering design. This work proposes a procedure to derive the elasto-plastic properties of metallic materials from the Vickers and the Knoop hardness measurements. Through dimensional analysis and finite-element simulations, relationships between hardness testing variables and mechanical parameters (Young's modulus, yield strength, and strain hardening exponent) are built up. An inverse procedure is developed to derive the mechanical parameters within the framework of genetic algorithm. The method is verified against two bulk steel materials and it is shown the derived stress-strain curves are in good accord with those measured by tensile tests. Then the method is successfully applied to measure the elasto-plastic properties of the pore walls of a metallic foam material. The present method can achieve a performance as good as those based on the instrumented indentation test and it is more readily accessible to the industry considering all the measurements can be performed on a cost-effective micro-hardness tester.