The magnetic field of the stator in a 3-phase motor rotates at a rate that is determined by the line frequency and by the number of poles. This rate is called the“synchronous speed.” With 60-Hertz power, this speed is 3,600 RPM for a 2-pole motor, 1,800 RPM for a 4-pole motor, 1,200 RPM for a 6-pole motor, etc. In single-phase motors, the synchronous speed is calculated the same way, even though the field does not actually rotate.