We propose that physical properties for the high temperature superconductors can be addressed by either a two-dimensional planar hole-doping concentration (P_<pl>) or an effective three-dimensional hole-doping concentration (P_<3D>). We find that superconducting transition temperature (T_c) exhibits a universal dome-shaped behavior in the T_c vs. P_<3D> plot with a universal optimal doping concentration at P_<3D> 〜 1.6 X 10^<21> cm^<−3> for the single-layer high temperature superconductors.
