Motor Torque Calculator

Calculate Motor Torque

Enter the motor’s power output.

Enter the motor’s speed at the shaft.

Enter the force applied tangentially.

Enter the distance from the axis of rotation to the point where force is applied.

What is a Motor Torque Calculator?

A motor torque calculator is a tool used to determine the rotational force (torque) produced by a motor based on its power and speed, or the force applied at a certain radius. Torque is a crucial parameter in motor selection and application design, as it dictates the motor’s ability to rotate a load.

Engineers, technicians, hobbyists, and students often use a motor torque calculator when designing systems involving electric motors, engines, or any rotating machinery. It helps ensure the selected motor can provide sufficient turning force for the intended task.

Common misconceptions include confusing torque with power or speed. While related, power is the rate at which work is done (how fast the torque can be applied over a distance), speed is the rotational velocity, and torque is the twisting force itself. A powerful motor torque calculator helps clarify these relationships.

Motor Torque Calculator Formula and Mathematical Explanation

There are two primary formulas used by a motor torque calculator, depending on the available input parameters:

1. Torque from Power and Speed:

The relationship between torque (T), power (P), and angular speed (ω) is given by: P = T * ω

If power is given in Watts (W) and speed in revolutions per minute (RPM), we first convert RPM to radians per second (rad/s): ω (rad/s) = N (RPM) * 2π / 60.

So, P = T * (N * 2π / 60). Rearranging for Torque (T) in Newton-meters (N.m):

T (N.m) = (P (W) * 60) / (2 * π * N (RPM))

Or approximately: T (N.m) ≈ 9.549 * P (W) / N (RPM)

If power is in Horsepower (HP), 1 HP = 745.7 Watts.

2. Torque from Force and Radius:

Torque is also defined as the product of the force applied tangentially and the distance from the axis of rotation (radius or lever arm):

T (N.m) = F (N) * r (m)

Where F is the force in Newtons and r is the radius in meters.

Our motor torque calculator uses these formulas based on your selection.

Variables Table

Variable	Meaning	SI Unit	Other Units	Typical Range
T	Torque	N.m (Newton-meter)	lbf.ft, oz.in, kgf.cm	0.001 – 10000+
P	Power	W (Watt)	kW, HP	1 – 100000+
N	Rotational Speed	RPM (Revolutions per minute)	rad/s	1 – 30000+
ω	Angular Speed	rad/s (Radians per second)	deg/s	0.1 – 3000+
F	Force	N (Newton)	lbf, kgf	0.1 – 100000+
r	Radius / Lever Arm	m (Meter)	cm, mm, in, ft	0.001 – 10+

Table of variables used in motor torque calculations.

Practical Examples (Real-World Use Cases)

Example 1: Using Power and Speed

Suppose you have an electric motor with a power rating of 2 kW running at 3000 RPM. You want to find the torque it produces.

• Power (P) = 2 kW = 2000 W
• Speed (N) = 3000 RPM

Using the formula T = (P * 60) / (2 * π * N):

T = (2000 * 60) / (2 * 3.14159 * 3000) ≈ 120000 / 18849.54 ≈ 6.366 N.m

The motor torque calculator would quickly give you this result.

Example 2: Using Force and Radius

Imagine you are tightening a bolt with a wrench. You apply a force of 50 N at the end of the wrench, which is 0.3 meters long.

• Force (F) = 50 N
• Radius (r) = 0.3 m

Using the formula T = F * r:

T = 50 N * 0.3 m = 15 N.m

This is the torque applied to the bolt. Our motor torque calculator can handle this too.

How to Use This Motor Torque Calculator

1. Select Calculation Method: Choose whether you have ‘Power & Speed’ values or ‘Force & Radius’ values using the radio buttons.
2. Enter Input Values:
   • If ‘Power & Speed’: Enter the power value and select its unit (W, kW, HP). Then enter the speed value and select its unit (RPM, rad/s).
   • If ‘Force & Radius’: Enter the force value and select its unit (N, lbf). Then enter the radius/lever arm value and select its unit (m, cm, in, ft).
3. View Results: The calculator automatically updates the ‘Calculated Torque’ in the results section as you enter values. The primary result is shown in N.m, with conversions to lbf.ft and kgf.cm also displayed.
4. Interpret Formula: The formula used for the calculation is shown below the results.
5. Reset: Click ‘Reset’ to return to default values.
6. Copy Results: Click ‘Copy Results’ to copy the input and output values to your clipboard.
7. Chart: The chart below the calculator visualizes the relationship between torque, speed, and power based on your current power input (if using power/speed mode).

Using the motor torque calculator correctly ensures you understand the rotational force your motor can deliver or the force required for your application.

Key Factors That Affect Motor Torque Results

Several factors influence the actual torque a motor can deliver or the torque required by a load:

• Input Power: For a given speed, higher power input generally results in higher torque output, as seen with our motor torque calculator.
• Rotational Speed: For a given power, torque is inversely proportional to speed. Higher speed means lower torque, and vice-versa.
• Motor Type and Design: Different motor types (DC, AC induction, brushless, stepper) have different torque-speed characteristics. The design (windings, materials) also plays a huge role.
• Voltage and Current: The electrical supply (voltage and available current) directly impacts the power and thus the torque a motor can produce, especially for electric motors.
• Load Characteristics: The nature of the load (constant torque, torque varying with speed, inertial loads) affects the required motor torque and how it’s delivered over time.
• Temperature: Motor windings heat up during operation, increasing resistance and potentially reducing efficiency and torque output. Ambient temperature also matters.
• Efficiency: Not all input power is converted to mechanical output power; some is lost as heat. Motor efficiency affects the actual torque delivered.
• Gearing: Gearboxes are often used to change the speed and torque between the motor and the load. A gearbox can increase torque while reducing speed (or vice versa), minus efficiency losses.

When using a motor torque calculator, remember it provides theoretical values based on the inputs. Real-world factors can influence the actual performance.

Frequently Asked Questions (FAQ)

What is torque in simple terms?

Torque is a twisting or turning force that tends to cause rotation. Think of it as the rotational equivalent of linear force.

Why is torque important for motors?

Torque determines a motor’s ability to start, accelerate, and maintain the rotation of a load. You need enough torque to overcome friction and inertia.

How does a motor torque calculator work?

It applies the fundamental physics formulas relating torque to power and speed (T = P/ω) or torque to force and radius (T = F*r), performing unit conversions as needed.

What’s the difference between starting torque and running torque?

Starting torque (or stall torque) is the torque produced by a motor when it is starting from rest. Running torque is the torque it produces at its normal operating speed.

Can I calculate torque from horsepower?

Yes, our motor torque calculator allows you to input power in horsepower (HP). 1 HP = 745.7 Watts, and the calculator converts it to Watts for the formula.

What if my motor has a gearbox?

If a gearbox with a ratio ‘G’ is used, the output torque is ideally G times the motor torque (and output speed is motor speed / G). However, gearboxes have losses, so the actual output torque will be slightly less.

How do I choose a motor with the right torque?

You need to determine the torque required by your load at its operating speed, including starting and acceleration phases. Then select a motor that can provide that torque, with some safety margin.

Does torque change with speed?

For a constant power output, torque is inversely proportional to speed. However, a motor’s ability to produce power and torque varies with its speed, as shown in its torque-speed curve.

Related Tools and Internal Resources

• Power Converter: Convert between Watts, kW, HP, and other power units.
• Speed Converter: Convert between RPM, rad/s, and other rotational speed units.
• Gear Ratio Calculator: Calculate output speed and torque with a gearbox.
• Ohm’s Law Calculator: Understand voltage, current, and resistance in electric motors.
• Work and Energy Calculator: Learn about the relationship between work, energy, and power.
• Force Calculator: Calculate force based on mass and acceleration.

Explore these tools for more in-depth calculations related to your motor torque calculator needs and engineering projects.