Calculator Inputs
Large screens show three columns, medium screens show two, and mobile screens show one.
Example Data Table
| Frequency (Hz) | Pole Count | Slip (%) | Gear Ratio | Synchronous RPM | Loaded RPM | Output RPM |
|---|---|---|---|---|---|---|
| 50 | 4 | 2.5 | 1.00 | 1500.00 | 1462.50 | 1462.50 |
| 60 | 6 | 3.0 | 2.00 | 1200.00 | 1164.00 | 582.00 |
| 25 | 8 | 1.5 | 1.50 | 375.00 | 369.38 | 246.25 |
| 75 | 2 | 4.0 | 3.00 | 4500.00 | 4320.00 | 1440.00 |
Formula Used
Synchronous speed: Ns = (120 × f) ÷ P
Ns is synchronous RPM, f is supply frequency in hertz, and P is the number of poles.
Loaded motor speed: Nm = Ns × (1 − s ÷ 100)
Nm is estimated running RPM and s is slip percentage.
Output shaft speed: Nout = Nm ÷ G
G is the gear ratio expressed as motor speed divided by output speed.
Reverse conversion: f = (Nout × G × P) ÷ (120 × (1 − s ÷ 100))
Use this when you know the required shaft RPM and want the matching supply frequency.
How to Use This Calculator
- Select the conversion mode that matches your task.
- Enter frequency or target output RPM.
- Choose the motor pole count.
- Enter the expected slip percentage.
- Add the motor-to-output gear ratio.
- Choose the number of decimal places.
- Press Calculate Result to show the result above the form.
- Use the export buttons to save the current result as CSV or PDF.
FAQs
1. What does the pole count change?
Pole count directly affects synchronous speed. More poles create lower RPM at the same frequency, while fewer poles create higher RPM.
2. Why is loaded RPM lower than synchronous RPM?
Induction motors require slip to produce torque. Because of slip, actual shaft speed stays slightly below theoretical synchronous speed during operation.
3. Can I use this for a VFD-driven motor?
Yes. Enter the applied output frequency from the drive, then add realistic slip and gearing values to estimate actual motor and output shaft speed.
4. What gear ratio format should I enter?
Use motor speed divided by output speed. For example, a 2:1 reduction means the motor turns twice for one output revolution, so enter 2.
5. Does this work for synchronous motors?
Yes. Set slip to zero. The loaded motor speed will match synchronous speed because an ideal synchronous motor locks to electrical frequency.
6. Can I estimate required frequency from target RPM?
Yes. Switch to RPM to Hz mode, enter target output RPM, and the calculator estimates the needed supply frequency after slip and gearing.
7. Is this suitable for generators and alternators?
It can help check the speed-frequency relationship. For generator studies, use slip as zero unless you are modeling a non-ideal rotating system.
8. Why include angular velocity and period?
These values help when translating motor speed into mechanical analysis, timing calculations, vibration studies, and coupling or flywheel design work.