In order to correlate hardness P_m by the spherical indenter with the flow stress Y, it is necessary to determine the total mean strain of the indentation, which corresponds to the total strain in a uniaxial stress field. Firstly, the total mean strain of the indentation ε_ic is defined, by means of multiplying the total corresponding strain coefficient of the indentation C_εc by the total profile coefficient of the indentation (d/D_c) at the end of the plastic flow of a specimen ; ε_ic=C_εc (d/D_c). Then Hardness/Flow stress ratio C is obtained experimentally, C=9.8 P_m/Y, Y in MPa, and formulated as follows ; C=1.1+(2/3) ln (ε_ic·E_s/Y), E_s is the Young's modulus of a specimen. Further, an example of the flow stress-strain characteristic curve of SUS 304 specimen is shown in a wide range of the strain by means of a calculation using this formula and the former reported formula ; P_m=P_up(d/D_p)^xp, etc..