A motor’s nameplate lists power and speed; torque follows directly. Induction motors run slightly slower than the rotating magnetic field – the slip, usually 1–5% – which is what lets them produce torque.
How to use the Electric Motor Torque Calculator
- Supply frequency
- Number of poles
- Motor speed (rpm)
- Output power
Results update as you type, every field has its own unit menu, and everything is calculated in your browser.
How it works
Enter the supply frequency, number of poles, actual motor speed and output power.
Inputs explained
| Field | What to enter |
|---|---|
| Supply frequency | Choose one: 50 Hz, 60 Hz |
| Number of poles | A number |
| Motor speed (rpm) | A number |
| Output power | Units: kW, W, hp |
What each result means
- Torque = [Output power]÷(2×pi×[Motor speed (rpm)]÷60)
- Synchronous speed = 120×[Supply frequency]÷[Number of poles]
- Slip = (120×[Supply frequency]÷[Number of poles] – [Motor speed (rpm)])÷(120×[Supply frequency]÷[Number of poles])×100
Example values
How the main result changes when Number of poles changes and everything else stays at the example values above:
| Number of poles | Torque (N·m) |
|---|---|
| 2 | 49.3929 |
| 3 | 49.3929 |
| 4 | 49.3929 |
| 5 | 49.3929 |
| 6 | 49.3929 |
| 8 | 49.3929 |
Formula
T = P / ω = 9549·P(kW) / n(rpm), n_s = 120·f / p, slip = (n_s − n)/n_s
Worked example
Inputs — Supply frequency: 50 Hz; Number of poles: 4; Motor speed (rpm): 1,450; Output power: 7.5 kW.
Results — Torque = 49.39291 N·m; Synchronous speed = 1,500 rpm; Slip = 3.333 %.
Key terms
- Synchronous speed
- Speed of the stator's rotating magnetic field.
Frequently asked questions
How do I find torque from kW and rpm?
T (N·m) = 9549 × P (kW) / n (rpm).
Why is the motor slower than synchronous speed?
Induction motors need slip to induce rotor current.
What is a 4-pole motor's synchronous speed at 50 Hz?
1,500 rpm.
Does torque change with load?
Yes – slip and torque rise together up to the breakdown point.