Electric Motor Torque Calculator
Calculate electric motor torque from power and speed using the standard formula T = 60P / (2π × rpm). Get synchronous speed, slip, interactive charts, and detailed breakdowns for AC and DC motors.
About This Calculator
The Electric Motor Torque Calculator computes the rotational force (torque) produced by an electric motor based on its power output and shaft speed. Whether you are sizing a motor for a pump, conveyor belt, fan, or industrial machinery, this tool helps you determine the torque at the operating speed using the fundamental power-torque relationship T = 60 × P / (2 × π × rpm).
For AC induction motors, the calculator also determines the synchronous speed — the rotational speed of the magnetic field — using the formula rpm_synch = 120 × f / p, where f is the supply frequency and p is the number of poles. The slip percentage, defined as the difference between synchronous speed and actual rotor speed divided by synchronous speed, is calculated to help evaluate motor loading and efficiency.
Torque is a critical parameter in motor selection. High-torque motors are needed for starting heavy loads, while lower-torque, high-speed motors suit fans and pumps. The calculator outputs torque in newton-metres (Nm), synchronous speed in rpm, and slip as a percentage. A detailed breakdown table shows all intermediate values, and interactive bar and pie charts visualise the motor performance characteristics.
Regional Notes
India: Standard supply frequency is 50 Hz. Common motor pole configurations are 4-pole (1500 rpm synchronous) and 2-pole (3000 rpm synchronous). Motor power is typically rated in kW (kilowatts) as per IS standards.
United States: Standard supply frequency is 60 Hz. A 4-pole motor has a synchronous speed of 1800 rpm, and a 2-pole motor runs at 3600 rpm. Motor power is often specified in horsepower (hp); 1 hp = 0.746 kW.
United Kingdom: Follows 50 Hz supply frequency like India. Motors are rated in kW, with 4-pole (1500 rpm) and 6-pole (1000 rpm) configurations common for industrial applications.
For accurate results, enter the motor's output power at the shaft (not input electrical power) and the actual operating speed under load, not the no-load speed.
Frequently Asked Questions
How is electric motor torque calculated?
Electric motor torque is calculated using the formula T = 60 × P / (2 × π × rpm), where P is the motor power in watts, rpm is the rotational speed, and T is the torque in newton-metres. For AC motors, synchronous speed is first computed as 120 × f / p, where f is the supply frequency and p is the number of poles.
What is slip in an AC motor?
Slip is the difference between the synchronous speed (magnetic field speed) and the actual rotor speed, expressed as a percentage of synchronous speed. It is calculated as s = (rpm_synch - rpm_load) / rpm_synch × 100%. Slip is essential for torque production in induction motors.
How do motor poles affect torque?
More poles in an electric motor result in lower synchronous speed and higher torque for the same power. For example, a 4-pole motor at 50 Hz has a synchronous speed of 1500 rpm, while a 2-pole motor at the same frequency runs at 3000 rpm. This is why high-torque, low-speed motors typically have more poles.
What is the difference between AC and DC motor torque?
DC motors produce high torque at low speeds, with torque decreasing as speed increases. AC induction motors reach their maximum torque (breakdown torque) at a specific slip value. Above that point, torque drops sharply toward zero at synchronous speed. AC motors never reach synchronous speed under load.
Can I use this calculator for any electric motor?
Yes, the torque formula T = 60P / (2π × rpm) applies to both AC and DC motors when you know the output power and shaft speed. For AC motors, the calculator also computes synchronous speed and slip when you provide the supply frequency and number of poles.
What units does this calculator use?
Power is entered in kilowatts (kW), motor speed in revolutions per minute (rpm), supply frequency in hertz (Hz), and torque is reported in newton-metres (Nm). Synchronous speed is given in rpm and slip as a percentage.
How does supply frequency affect motor torque?
Supply frequency determines the synchronous speed of an AC motor. At 50 Hz (common in India, UK, Europe, Australia), a 4-pole motor has a synchronous speed of 1500 rpm. At 60 Hz (common in the US, Canada, parts of South America), the same motor has a synchronous speed of 1800 rpm. Higher frequency increases speed but reduces available torque for the same power.
What is breakdown torque?
Breakdown torque is the maximum torque an AC induction motor can produce. It occurs at a specific slip value, typically between 10–20%. Beyond this point, the torque decreases rapidly. Manufacturers specify breakdown torque in motor datasheets along with the corresponding slip percentage.