Torque Calculator
Calculate shaft torque from motor power, rotational speed, and efficiency.
Calculated Torque
0 N·m
0 kgf·m
0 lb-ft
Formula used:Torque (N·m) = (9550 × Power in kW × Efficiency) ÷ RPM
Torque Formula
The most common formula for calculating rotational torque from motor power and speed is:
Where:
- T = Torque in Newton-metre (N·m)
- P = Power in kilowatts (kW)
- N = Rotational speed in RPM
The constant 9550 converts RPM and power in kW into torque in Newton-metre. The fundamental relationship is:
Example: Torque of a 15 kW Motor at 1,440 RPM
Given:
- Motor power = 15 kW
- Motor speed = 1,440 RPM
Therefore, the motor shaft torque is approximately: 99.5 N·m
Other Torque Formulas
Torque from Force and Lever Radius
Where:
- T = Torque in N·m
- F = Applied force in Newtons (N)
- r = Perpendicular distance from shaft centre in metres (m)
Example: A force of 200 N acts at a radius of 0.5 m.
Torque Formula When Power Is in Watts
Where:
- P = Power in watts (W)
- N = Speed in RPM
- T = Torque in N·m
Torque Formula When Power Is in Horsepower
Where:
- T = Torque in N·m
- HP = Metric horsepower
- N = Speed in RPM
Torque with Drive Efficiency
For gearbox, belt-drive, chain-drive, or coupling systems, account for overall transmission efficiency:
Where:
- Toutput = Output torque in N·m
- Pmotor = Motor power in kW
- η = Overall drive efficiency, expressed as a decimal
- Noutput = Output speed in RPM
For example, 90% efficiency must be entered as 0.90, and 95% efficiency as 0.95.
Torque is the turning or twisting force that makes an object rotate. In mechanical systems, torque is produced by motors, engines, gearboxes, hand levers, and rotating machines. It is essential when designing or selecting shafts, couplings, gears, pulleys, belts, chains, bearings, pumps, conveyors, fans, and other power-transmission components.
A Shaft is a rotating mechanical member, usually round in cross-section, that transfers rotary motion, torque, and power from one component to another. For example, an electric motor shaft may drive a pulley, gearbox, gear, pump, compressor, fan, or conveyor. Shafts are designed to safely transmit torque while resisting torsional stress, bending, vibration, and fatigue.
Power is the rate at which work is done or energy is transmitted. In a rotating machine, power depends on two main values: torque and speed. A machine may produce high torque at low RPM, or lower torque at high RPM, while transmitting the same power. The basic relationship is:
Power = Torque × Angular Velocity
This calculator uses motor or shaft power in kilowatts (kW), rotational speed in revolutions per minute (RPM), and optional efficiency (%) to estimate torque. It applies the standard relationship:
Torque (N·m) = (9550 × Power in kW × Efficiency) ÷ RPM
Enter the rated or actual delivered power, shaft speed, and transmission efficiency. Use 100% efficiency for a direct theoretical calculation. For a gearbox, belt drive, chain drive, or coupling system, enter the estimated overall efficiency.
The calculator provides torque in three commonly used units:
Newton-metre (N·m): The standard SI unit used in mechanical design, motors, shafts, couplings, and engineering drawings.
Kilogram-force metre (kgf·m): A traditional metric unit still found in older machinery manuals and some equipment catalogues.
One kgf·m equals 9.80665 N·m.
Pound-foot (lb-ft): A common imperial/US torque unit used in automotive, engines, fasteners, and international equipment documentation.
One N·m is approximately 0.737562 lb-ft.
This tool is useful for preliminary motor selection, shaft design, gearbox output checks, coupling selection, and mechanical power-transmission calculations. For final design, also consider starting torque, peak load, shock loading, service factor, speed reduction ratio, actual efficiency, bending moment, material strength, shaft diameter, keyway effects, fatigue life, and applicable engineering standards.