PangPang Tools60 Hz; 4 poles
Synchronous speed 1,800 rpm; 3,600 cycles/min; 2 pole pairs120 × 60 ÷ 4 = 1,800 rpm. A four-pole induction motor generally runs below this under load.
Construction & Electrical
AC motor synchronous speed calculator
About this tool
The rotating magnetic field of an AC motor has a synchronous speed set by the electrical frequency and the number of magnetic poles. The formula is rpm = 120 × frequency (Hz) ÷ poles. This tool also displays electrical cycles per minute and the number of pole pairs. It estimates field speed, not the actual loaded shaft rpm of an induction motor, which runs slightly slower because of slip.
Motor speed & shaft torque
Choose a task. Inputs stay in this page only.
MAKE IT SIMPLE
Result
Worked examples
50 Hz; 6 poles
Synchronous speed 1,000 rpm; 3,000 cycles/min; 3 pole pairs120 × 50 ÷ 6 = 1,000 rpm. Changing pole count or frequency changes the rotating-field speed.
Questions & answers
Why is the nameplate rpm lower than this result?
For an induction motor, slip is required to produce torque; the rotor commonly turns below the rotating field's synchronous speed.
What frequency should I enter for a VFD-fed motor?
Use the drive's actual output electrical frequency at the operating point, not necessarily the fixed utility mains frequency.
MAKE IT SIMPLE
Result
Worked examples
Shaft output (kW): 5.5, Shaft speed (rpm): 1750
Torque: 30.012075 N·mUsing these sample input values gives the first labelled output above. Enter actual mechanical shaft output rather than electrical input power.
Questions & answers
Can I use the default numbers for purchasing or safety certification?
No. Replace the examples with your real values. Enter actual mechanical shaft output rather than electrical input power.