⚡ Electric Motor Torque Calculator
Calculate motor torque from power and speed
Enter mechanical power output. Example: 746 W = 1 HP
Rotational speed in revolutions per minute
How to Use This Calculator
Enter Power
Input the mechanical power output of the motor in Watts. You can convert horsepower to watts: 1 HP = 746 W. This is the actual mechanical power delivered by the motor, not the electrical input power.
Enter Speed
Input the rotational speed of the motor in revolutions per minute (RPM). This is typically specified on the motor nameplate or can be measured with a tachometer.
Calculate
Click the "Calculate Torque" button to get the motor torque in Newton-meters (N⋅m) and pound-feet (lb⋅ft).
Formula
T = P / ω
where ω = 2π × RPM / 60
Where:
- T = Torque (Newton-meters, N⋅m)
- P = Power (Watts, W)
- ω = Angular Velocity (radians per second, rad/s)
- RPM = Rotational Speed (revolutions per minute)
Alternative Form:
T = (P × 30) / (π × RPM)
Example Calculation:
For a 1 HP (746 W) motor running at 1750 RPM:
ω = 2π × 1750 / 60 = 183.26 rad/s
T = 746 / 183.26 = 4.07 N⋅m
T = 3.00 lb⋅ft
Note: This calculates torque at steady-state operation. Starting torque and peak torque may differ significantly.
About Electric Motor Torque Calculator
The Electric Motor Torque Calculator determines the torque output of an electric motor based on its power rating and rotational speed. Torque is the rotational force that enables a motor to do work, and understanding the relationship between power, speed, and torque is essential for motor selection and application design.
When to Use This Calculator
- Motor Selection: Calculate required torque to select appropriate motors for specific applications
- System Design: Determine torque requirements for mechanical systems and drive trains
- Performance Analysis: Analyze motor performance and verify torque output at different speeds
- Gearbox Design: Calculate torque at different speeds when designing gear reduction systems
- Academic Study: Understand the relationship between power, speed, and torque in rotating systems
Why Use Our Calculator?
- ✅ Quick Calculation: Instantly determine torque from power and speed
- ✅ Dual Units: Results in both metric (N⋅m) and imperial (lb⋅ft) units
- ✅ Motor Applications: Essential for motor selection and system design
- ✅ Free Tool: No registration or payment required
- ✅ Educational: Learn the fundamental power-torque-speed relationship
Common Applications
Industrial Motors: Select appropriate motors for industrial applications like pumps, conveyors, and fans, where understanding torque at operating speed is crucial for proper motor sizing and avoiding overload conditions.
Automotive Applications: Calculate torque requirements for electric vehicle motors and understand how power and speed relate to wheel torque, essential for vehicle performance and battery efficiency calculations.
Robotics and Automation: Determine torque requirements for robotic joints and actuators, ensuring motors provide sufficient torque for the required motion while operating at appropriate speeds.
Tips for Best Results
- Use mechanical output power, not electrical input power (account for motor efficiency if needed)
- Torque is inversely proportional to speed for constant power: lower speed = higher torque
- Starting torque is typically higher than running torque for most motors
- For variable speed applications, torque may vary with speed depending on motor type
- Consider efficiency losses when converting from electrical power to mechanical power
Frequently Asked Questions
What is the relationship between power, torque, and speed?
Power = Torque × Angular Velocity (P = Tω). For constant power, torque and speed are inversely related - doubling speed halves torque, and vice versa. This is why high-torque applications often use gear reduction to lower speed.
Is this the same as starting torque?
No, this calculates steady-state running torque at the specified speed. Starting torque (locked-rotor torque) is typically 150-300% of full-load torque for induction motors and can be much higher for other motor types.
How do I convert horsepower to watts?
1 horsepower (HP) = 746 watts (W). For metric horsepower, 1 HP = 735.5 W. Simply multiply horsepower by 746 to get watts for use in this calculator.
Does motor efficiency affect torque?
Yes, indirectly. Use mechanical output power (not electrical input) for accurate torque calculation. If you have electrical input power, multiply by motor efficiency (typically 0.7-0.95) to get mechanical power: P_mech = P_elect × efficiency.
What if my motor has variable speed?
For variable frequency drives (VFDs), torque typically remains constant up to base speed, then power remains constant above base speed (constant power region). Calculate torque for each operating speed using this calculator.
How do I use this for gearbox selection?
Calculate the required output torque, then divide by gear ratio to find motor torque needed. Motor speed will be output speed × gear ratio. Select a motor that provides the calculated torque at that speed.