Motor Torque Calculator

Calculated Motor Torque

9.55 N·m

Intermediate Values:

Power: 1500.00 Watts

Angular Velocity: 157.08 rad/s

Torque (ft-lb): 7.04 ft·lb

Torque vs. Speed Curve (at 1.5 kW)

Chart showing the inverse relationship between speed and torque for a constant power output.

What is a Motor Torque Calculator?

A motor torque calculator is a tool used to determine the rotational force, or torque, that a motor produces based on its power output and rotational speed. Torque is a crucial parameter in engineering and mechanics, as it quantifies a motor’s ability to do work, such as turning a wheel, a gear, or a pulley. Understanding motor torque is essential for correctly sizing and selecting a motor for any application, from small robotics to large industrial machinery. This calculator helps bridge the gap between abstract specifications like power and the tangible turning force the motor delivers.

Motor Torque Formula and Explanation

The relationship between power, speed, and torque is fundamental in physics. The most common formula used for this calculation, especially in engineering contexts, is:

Torque (N·m) = 9.5488 * Power (kW) / Speed (RPM)

This formula directly relates power in kilowatts (kW) and speed in revolutions per minute (RPM) to torque in Newton-meters (N·m). The constant 9.5488 is a conversion factor derived from unifying the units (kW and RPM) into the base SI units of watts and radians per second.

Variables Table

Variable	Meaning	Unit (in formula)	Typical Range
Torque (T)	The rotational force produced by the motor.	Newton-meters (N·m)	0.1 – 10,000+ N·m
Power (P)	The rate at which the motor performs work.	Kilowatts (kW)	0.01 – 5,000+ kW
Speed (n)	The rotational speed of the motor shaft.	Revolutions per Minute (RPM)	100 – 20,000 RPM

Practical Examples

Example 1: Standard Industrial Motor

Imagine you have a standard industrial motor for a conveyor belt with the following specifications:

• Inputs: Power = 2.2 kW, Speed = 1750 RPM
• Calculation: Torque = 9.5488 * 2.2 / 1750
• Results: The motor produces approximately 12.00 N·m of torque. This value is critical for ensuring the motor can handle the conveyor’s load.

Example 2: High-Speed Hobby Motor (with unit conversion)

Consider a high-performance RC car motor with these specs:

• Inputs: Power = 0.5 hp, Speed = 10,000 RPM
• Unit Conversion: First, convert horsepower to kW (0.5 hp ≈ 0.373 kW).
• Calculation: Torque = 9.5488 * 0.373 / 10000
• Results: The motor produces a much smaller torque of 0.36 N·m, which is typical for high-speed, low-force applications.

How to Use This Motor Torque Calculator

1. Enter Motor Power: Input the power rating of your motor into the “Motor Power” field.
2. Select Power Unit: Use the dropdown to choose the correct unit for your power value: Kilowatts (kW), Watts (W), or Horsepower (hp). The calculator will handle the conversion automatically.
3. Enter Rotational Speed: Input the speed of the motor in Revolutions per Minute (RPM).
4. Review the Results: The calculator instantly displays the primary torque result in Newton-meters (N·m). It also shows intermediate values like power in watts and torque in an alternative unit (ft-lb) for your convenience.
5. Analyze the Chart: The dynamic chart visualizes how torque changes at different speeds for the entered power level, illustrating the inverse relationship.

Key Factors That Affect Motor Torque

The torque a motor can produce isn’t just about power and speed; several design and operational factors play a crucial role.

• Current: In DC motors, torque is directly proportional to the current flowing through the windings. More current generally means more torque.
• Magnetic Field Strength: A stronger magnetic field (from either permanent magnets or electromagnets) exerts a greater force on the rotor, leading to higher torque.
• Motor Windings: The number of turns in the wire coils (windings) directly influences torque. More turns amplify the magnetic force.
• Gearing: While not a factor of the motor itself, gearboxes are often used to multiply torque. A gear reducer decreases speed but increases the output torque.
• Operating Temperature: Excessive heat can increase electrical resistance and reduce the efficiency of the motor, leading to a drop in torque output.
• Voltage: Voltage is more directly related to motor speed, but it affects the current the motor can draw, which in turn impacts torque.

For more detailed information, our Ohm’s Law Calculator can help you understand the relationship between voltage, current, and resistance.

Frequently Asked Questions (FAQ)

What is the difference between motor torque and power?

Power is the rate at which work is done, while torque is the capacity to do that work. A motor can have high power but low torque (like a dentist’s drill) or low power and high torque (like a winch). Power is calculated from torque and speed.

Why does torque decrease as speed increases for a constant power?

Since Power = Torque × Angular Speed, if power is held constant, an increase in speed must be balanced by a decrease in torque. This is the inverse relationship you see on the calculator’s chart.

What is “stall torque”?

Stall torque is the maximum torque a motor can produce when its rotational speed is zero (i.e., when it is stalled or not turning). This is an important metric for applications requiring high starting force.

How do I convert torque from N·m to ft-lb?

To convert Newton-meters to foot-pounds, you multiply the N·m value by approximately 0.73756. Our calculator provides this conversion automatically.

Can I calculate torque from force and radius?

Yes. Torque is also defined as Force × Radius (T = F × r). This formula is often used when calculating the load torque required in an application, such as lifting a weight with a pulley.

Does the motor type (AC vs. DC) change this calculation?

No, the fundamental relationship between power, speed, and torque is the same regardless of motor type. However, the internal factors affecting torque, like current and voltage, behave differently in AC and DC motors.

What is a good torque value for an electric bike?

A typical mid-drive electric bike motor produces between 50 and 90 N·m of torque. This provides enough force for climbing hills and quick acceleration. You can explore more with our Power to Weight Ratio Calculator.

Why is my motor getting hot when under load?

When a motor is under a heavy load, it draws more current to produce the required torque. This increased current flow through the windings generates more heat due to electrical resistance (I²R losses). Proper cooling is crucial to prevent overheating and damage.