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Stepper Motor Current & Torque Calculator

Estimate holding torque, electrical time constant, and the corner step frequency where inductance starts limiting available torque, from a stepper motor's datasheet parameters.

Phase resistance1.50 ΩPhase inductance3.0 mHRated phase current1.50 ATorque constant (K_t)0.10 Nm/AFull steps per revolution200

R and L are per-phase datasheet values. K_t is the motor's torque constant (often listed as holding torque at rated current, from which K_t = T / I).

Holding torque

0.150 Nm

T_hold = K_t × I

Electrical time constant

2.00 ms

τ = L / R

Corner step frequency

79.6 Hz

f_corner = R / (2π × L)

Approx. corner speed

23.9 RPM

RPM = f_corner × 60 / steps_rev

T_hold = Kt × I

τ = L / R

f_corner = R / (2π × L)

RPM_corner = f_corner × 60 / steps_per_rev

Above the corner frequency, winding inductance limits how fast current can build each step, so available torque falls off with speed even though the driver is still commanding full current.

References

Typical two-phase bipolar stepper driver datasheets (e.g. Allegro A4988, TI DRV8825) — electrical time constant and torque roll-off with step rate