A compressor control method includes providing variable aerodynamic sizing of fluid flow through a compressor at multiple operating points of the compressor. A head is determined for an operating point, based on a process input at that operating point. Further, for that operating point, a control pressure number is determined as a function aerodynamic flow sizing at that operating point. The control pressure number is determined a function of the head divided by the square of a tip speed of the impeller of the compressor. An operating speed setpoint is determined based on the determined head and control pressure number.