NM = (60 * P) / (2 * π * RPM)
P = (NM * 2 * π * RPM) / 60
Where：
NM = Torque (N·m)
P = Power (W)
RPM = revolutions/minute
π = 3.1415926535
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.
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.
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.
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.
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.
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.
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 |
|---|---|
| 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 |
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.
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.
This calculator serves engineers, technicians, and students across mechanical and electrical engineering disciplines, including:
Mechanical Design Engineers: Calculating drive requirements for conveyors, automation systems, and robotic joints.
Electrical & Automation Engineers: Specifying motors, VFDs, and servo drives according to mechanical load profiles.
Maintenance & Reliability Technicians: Troubleshooting overloaded motors, mechanical jams, and power transmission failures.
Engineering Students & Educators: Validating physics problems involving angular kinematics, torque-speed curves, and rotational dynamics.
When sizing drives or calculating shaft output, account for real-world losses and transient conditions using these parameters:
Gearbox & Mechanical Efficiency (η): Direct drive shafts operate near 98% efficiency, helical gearboxes range from 92% to 97%, while worm gearboxes can drop to 50%-85%. Always divide required output power by η to find motor input power.
Starting / Locked-Rotor Torque: Induction motors often produce starting torque 1.5 to 2.5 higher than rated full-load torque. For high-inertia loads (e.g., crushers, flywheels), ensure the peak motor torque exceeds load requirements.
Variable Frequency Drive (VFD) Constant Torque vs. Constant Power: Below base speed, motors deliver constant torque (power increases linearly with RPM). Above base speed (field weakening), motors deliver constant power (torque decreases inversely with RPM).
This calculator computes mechanical power (P), torque (T), or rotational speed (n/ω) for rotating mechanical and electrical machinery, such as electric motors, gearboxes, pumps, and turbines. It seamlessly converts between Metric (SI) and Imperial units, supporting power in kilowatts (kW), watts (W), or horsepower (hp); torque in Newton-meters (N⋅m), pound-feet (lb⋅ft), or pound-inches (lb⋅in); and rotational speed in revolutions per minute (RPM) or radians per second (rad/s).
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