The results of experimental studies of the acoustic impedance of orifices in the plate in the impedance tube, using the transfer functions method in a wide range of sound pressure levels, are presented. Dependencies of the orifice impedance on its diameter in nonlinear regimes are obtained. It is established that in order to obtain reliable estimates of the orifice impedance, the particle velocity in the orifice should be determined by measurements. It is shown that the diameter of the orifice does not affect its acoustic impedance in the developed nonlinearity regimes. This impedance depends only on the particle velocity in the orifice, and this dependence is nonlinear.