Stepper Motor Torque Explained: How to Calculate and Select the Right Torque

Stepper motor torque is a crucial factor in determining how well a stepper motor will perform in a given application.
It refers to the rotational force that the motor produces to move or hold a load.
In this article, we will explain what stepper motor torque is, how it is calculated, and how to select the appropriate torque for your system.

What is Stepper Motor Torque?

Torque is the rotational force that a stepper motor generates to perform mechanical work.
It is typically measured in **Newton-meters (Nm)** or **ounce-inches (oz-in)**.
The torque produced by a stepper motor determines its ability to move a load or keep a position under load.
For example, if a motor has a high torque, it can handle heavier loads or perform tasks requiring more force, such as turning larger wheels or actuating linear motion.

How is Stepper Motor Torque Calculated?

Torque in a stepper motor is a function of several factors, including motor size, step angle, current, and voltage.
In general, torque is proportional to the current supplied to the motor. The more current the motor receives, the more torque it will produce.
However, it is also affected by other parameters such as the motor’s frame size, step angle, and speed.

Torque vs Current

One of the primary ways to control the torque in a stepper motor is by adjusting the current.
As the current increases, the motor’s torque capacity also increases, allowing it to handle more substantial loads.
However, this also generates more heat, which may require cooling mechanisms to maintain efficiency.

Factors That Affect Stepper Motor Torque

Several factors influence the torque a stepper motor can produce:

Current: As mentioned, higher current increases torque, but also generates more heat.
Motor Size: Larger motors, such as NEMA 23, generally produce higher torque than smaller motors like NEMA 17.
Step Angle: The smaller the step angle, the more precise the motor’s movement. Smaller steps also mean more torque is required to move each step.
Speed: Torque decreases as the speed of the motor increases. For high-speed applications, you may need to increase the motor size or use a higher voltage driver.
Load: The torque requirement increases with the weight and inertia of the load the motor is driving.

How to Calculate Stepper Motor Torque

To calculate the required torque for your stepper motor, you need to know the following parameters:

Load weight (in kilograms or pounds)
Load inertia
Required speed
Motor step angle and current rating

A common approach is to use the formula:

Torque (Nm) = Force (N) × Distance (m)

Where Force is the load applied to the motor (calculated from the weight of the object), and Distance is the radius of the motor shaft or the point of application.

Step-by-Step Torque Comparison

Motor Model	Holding Torque (Nm)	Peak Torque (Nm)	Recommended Speed (RPM)	Frame Size
NEMA 17 – 2A	0.45 Nm	0.6 Nm	1000 RPM	NEMA 17
NEMA 23 – 4A	1.2 Nm	1.5 Nm	1500 RPM	NEMA 23
NEMA 34 – 6A	2.5 Nm	3.2 Nm	1800 RPM	NEMA 34

Compare different motor models based on holding torque, peak torque, speed, and frame size to choose the right motor for your application.

Factors Affecting Stepper Motor Torque

The torque generated by a stepper motor can be influenced by several factors. Understanding these factors is essential for selecting the right motor for your application. Below are the key factors that impact stepper motor torque:

Current: Higher current increases the torque, but it also generates more heat, which could affect motor efficiency and lifespan.
Motor Size: Larger motors generally produce higher torque. For example, NEMA 23 motors typically provide more torque than NEMA 17 motors.
Step Angle: A smaller step angle provides finer resolution, but it also requires more torque to make each movement.
Load: The heavier the load, the more torque is required. Be sure to calculate the total load your motor needs to move or hold.
Speed: Torque generally decreases as speed increases. For high-speed applications, a motor with higher torque and a larger frame may be necessary to maintain performance.

Understanding how each of these factors influences your motor’s performance will help you select the right motor for your specific needs.

Calculate Your Required Stepper Motor Torque

Use the tool below to calculate the required torque for your application.

Tip: For stepper motors, effective radius is usually 0.01–0.03 m (10–30 mm).

How to Choose the Right Torque for Your Stepper Motor?

When selecting a stepper motor for your application, it’s essential to choose a motor that provides enough torque to handle the load while avoiding excessive torque, which can lead to overheating and inefficiency. Below are some guidelines for selecting the right torque:

Estimate the load: Calculate the weight and inertia of the object the motor will drive.
Consider the speed requirements: Higher speeds typically require more torque, so you need to select a motor capable of delivering the required performance.
Choose a motor with sufficient torque: The motor’s torque rating should exceed the calculated load torque to ensure reliable operation. A good rule of thumb is to choose a motor that provides 20-30% more torque than the calculated load.

Why Stepper Motor Wiring Matters for Torque Performance

Although torque calculations provide a theoretical reference, actual motor performance depends heavily on wiring configuration. For instance, a 4-wire bipolar stepper motor delivers torque differently compared to a 6-wire motor wired in unipolar mode. Therefore, understanding wiring diagrams is essential before final motor selection.

If you are not familiar with motor wiring types, read our detailed guide: Stepper Motor Wiring Diagram, which explains 4-wire, 6-wire, and 8-wire stepper motor wiring step by step.

Common Applications of Stepper Motor Torque

Stepper motors are used in a wide variety of applications, where precise movement and torque are required. Some common applications include:

CNC machines: Stepper motors provide precise control over milling, cutting, and engraving operations.
Robotics: For robotic arms, pick-and-place machines, and motion platforms, stepper motors are used to drive joints and actuators with high accuracy.
3D printers: Stepper motors ensure accurate movement along the X, Y, and Z axes during printing operations.
Medical equipment: In medical devices like liquid dispensers and sample positioning systems, precise torque is crucial for accurate operation.

Final Thoughts

Choosing the right stepper motor torque is essential for ensuring your system runs smoothly and efficiently.
By understanding how torque is calculated and considering the various factors that influence motor performance, you can make an informed decision when selecting a stepper motor for your application.

For more detailed guidance and to explore our stepper motor solutions, you can browse our
Stepper Motor product category
or contact us for technical support.