Enter the motor torque constant (N·m/A) and the phase current (amps per phase) into the calculator to estimate the stepper motor torque. This is an idealized, low-speed estimate and does not account for torque drop with speed, driver current regulation details, wiring (series/parallel), or excitation mode (1-phase on, 2-phase on, microstepping).

Stepper Motor Torque Calculator

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Stepper Motor Torque Formula

The following formula can be used to estimate stepper motor torque from a torque constant and phase current, assuming the motor is operating in its approximately linear region and the torque constant is defined for the same excitation method.

T_{sm} \approx K_T \cdot I_{ph}
  • Where Tsm is the estimated stepper motor torque (N·m)
  • KT is the torque constant for your definition (N·m/A)
  • Iph is the phase current (A, per phase)

To estimate torque, multiply the torque constant by the phase current. If you only have datasheet holding torque (Thold) at a rated phase current (Irated), a common approximation is KT ≈ Thold/Irated using the same wiring and excitation mode. Real available torque depends strongly on speed and drive conditions, so use the motor’s torque-speed curve for design work.

How to Calculate Stepper Motor Torque?

The following two example problems outline how to estimate the Stepper Motor Torque using the relationship above.

Example Problem #1:

  1. First, determine the torque constant (N·m/A). In this example, the torque constant is 0.25 N·m/A.
  2. Next, determine the phase current (A, per phase). For this problem, the phase current is 2.0 A.
  3. Finally, calculate the estimated torque using the formula above: 

Tsm ≈ KT·Iph

Inserting the values from above and solving the equation with the input values gives: 

Tsm ≈ 0.25*2.0 = 0.50 (N·m)

Example Problem #2: 

Using the same process as example problem 1, we first define the variables outlined by the formula. In this case, the values are:

torque constant (N·m/A) = 0.18

phase current (A, per phase) = 1.5

Entering these values yields:

Tsm ≈ 0.18*1.5 = 0.27 (N·m)