Electric Motor Torque Calculator - Power, RPM, and Slip

What Is Electric Motor Torque?

Electric motor torque is the rotational force the shaft delivers. It links shaft power and speed: a motor with more power at the same RPM produces higher torque, while higher speed at fixed power lowers torque.

Torque Formulas

For metric inputs with power in kilowatts:

$$T = \frac{9550 \times P_{\text{kW}}}{\text{rpm}}$$

For imperial inputs with power in horsepower:

$$T = \frac{5252 \times \text{HP}}{\text{rpm}}$$

The general relationship from shaft power in watts is:

$$T = \frac{60 P}{2\pi \times \text{rpm}}$$

For AC motors, synchronous speed depends on supply frequency and pole count:

$$\text{rpm}_{\text{synch}} = \frac{120 f}{p}$$

Example: 1 kW at 1800 rpm gives about 5.31 N·m. A 4-pole motor on 60 Hz has synchronous speed 1800 rpm.

Frequently Asked Questions

What is the difference between torque and power?

Power is the rate of doing work. Torque is the twisting force on the shaft. At higher RPM, the same power corresponds to lower torque.

When should I use the 9550 formula?

Use it when shaft power is in kilowatts and you want torque in newton-meters. It is a convenient rearrangement of the general power-speed relation.

Why does a 4-pole motor run near 1800 rpm on 60 Hz?

Synchronous speed is 120 times frequency divided by pole count, which is 1800 rpm. Real loaded speed is slightly lower because of slip.

What is motor slip?

Slip is the percent difference between no-load speed and loaded speed. It shows how far the rotor runs below synchronous speed under load.

Do DC and AC motors use the same torque formula?

Yes for the power-speed relation. AC motors also need pole count and frequency to estimate synchronous speed and breakdown torque behavior.

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Electric Motor Torque

What Is Electric Motor Torque?

Torque Formulas

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