Torque and Power Calculator for Rotating Systems
Calculate torque (N·m, ft·lbf) or power (kW, HP) from RPM using the mechanical power-torque-speed relationship. Supports motors, engines, pumps, turbines, and gear systems for engineering design and analysis.
This tool calculates torque (T) in rotating mechanical systems using power (P) and rotational speed (n). It is commonly used in mechanical engineering for sizing drives, gears, couplings, and transmission components.
Commonly used in mechanical engineering and motor selection for sizing drives, gears, and transmission systems.
How Do You Calculate Torque from Power and RPM?
Use the following formula:
T = P × 9549 / n
Where:
T = Torque (N·m)
P = Power (kW)
n = Rotational speed (rpm)
For power in horsepower (HP), use:
T = P × 5252 / n
Where P is in HP.
What Is the Formula for Motor Torque?
The standard formula for calculating torque in rotating machinery is:
- SI units: T = P × 9549 / n (N·m)
- Imperial units: T = P × 5252 / n (ft·lbf)
Where P is power in kW or HP, and n is RPM.
What Is the Unit of Torque?
The SI unit is Newton-meter (N·m). Other common units include:
- kgf·m (kilogram-force meter)
- ft·lbf (foot-pound force)
- in·lbf (inch-pound force)
This calculator supports all four units for easy conversion.
Is Torque Directly Proportional to Power?
Yes, but only when speed is constant. Torque is directly proportional to power and inversely proportional to speed. For a given power output, increasing speed reduces torque, and vice versa.
How Does Torque Relate to Speed in an Electric Motor?
In electric motors, torque and speed have an inverse relationship at constant power:
- At low speed: high torque (e.g., startup)
- At high speed: low torque (e.g., steady-state operation)
This is why motors are often designed with specific torque-speed curves for different applications.
What Is Rated Torque vs Peak Torque?
Rated torque is the continuous torque a motor can deliver at full load without overheating. It corresponds to the rated power and speed.
Peak torque is the maximum torque a motor can produce momentarily (e.g., during acceleration). It is typically higher than rated torque but not sustainable.
Parameter Description
| Parameter | Description |
|---|---|
| Calculation Mode | Select whether to calculate torque from power and RPM, or power from torque and RPM. |
| Power | Mechanical power output of the motor. Units: kW, HP, W |
| Revolutions (RPM) | Rotational speed of the motor shaft in revolutions per minute. |
| Torque | Rotational force produced by the motor. Units: N·m, kgf·m, ft·lbf, in·lbf |
Torque Calculation Principle
The fundamental relationship between torque, power, and speed is:
T = P × 9549 / n
Where:
- T = Torque (N·m)
- P = Power (kW)
- n = Rotational speed (rpm)
Note: This assumes constant power output and ideal conditions. For AC motors, this typically represents the rated torque at full load.
Usage Recommendations
- Use this tool to size motors, gearboxes, and couplings
- Convert between metric and imperial units for international projects
- Verify motor specifications before installation
- Ensure torque values match application requirements (e.g., conveyor, pump, fan)
This calculator adheres to ISO standards and supports accurate torque analysis in real-world mechanical systems.
