We studied the hole concentration dependences of 63 Cu Knight shifts in single-CuO 2 -layer high-T c cuprate superconductors HgBa 2 CuO 4+δ and double-layer HgBa 2 CaCu 2 O 6+δ . We found that the spin Knight shift at room temperature as a function of the hole concentration in the single-layer superconductor is different from that in the double-layer superconductor. Two type relations between the spin Knight shift and the hole doping level serve to estimate the individual hole concentrations of the non-equivalent CuO 2 planes in a unit cell.