Motor Current Estimator

Estimate DC motor current from voltage, power, torque (Kt/Kv), and winding resistance. Includes stall estimate + Show Work.

How to Use

  1. Pick a method (Power, Torque/Kt, or Resistance/Stall).
  2. Enter the values you know (leave unknowns blank).
  3. Read the live estimates and open “Show Work” for steps.
  4. Use “Share Link” only when you want a URL with your inputs.
Motor Lab View
Quick readout for current, power, torque, and stall estimate.
I (Run)
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I (Stall)
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P (Elec)
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τ (Torque)
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Risk: —
Supply DC Motor Load Use inputs to estimate run + stall current. Visuals scale with current & heat. Visuals scale with estimated current (flow speed) and heating (overlay).
Inputs & Settings
Enter what you know. The estimator will use the best available method based on your mode + inputs.
Battery/PSU voltage feeding the motor.
If you know watts: I ≈ P / V (run estimate).
If you know torque + Kt, estimate current: I ≈ τ / Kt.
If you only know Kv, the tool can convert (approx.).
Optional: used to estimate Kt (approx.) if Kt is blank.
Stall current: Istall ≈ V / R (ideal, ignores driver limits).
Show Work (step-by-step)
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Work is shown in base units (V, A, Ω, W, N·m) for clarity. Conversions are displayed when used.

Reference

  • From Power: I ≈ P / V (electrical input estimate)
  • From Torque: I ≈ τ / Kt (DC motor torque constant)
  • Stall (ideal): Istall ≈ V / R (ignores driver limits & wiring drop)
  • Kv → Kt (approx): Kt (N·m/A) ≈ 60 / (2π·Kv(rpm/V))

Real motors can draw less or more depending on controller limits, wiring drop, back-EMF, temperature, and load dynamics.

FAQ

Is stall current safe to use for fuse sizing?

It’s a useful worst-case reference, but use controller limits and real measurements when possible. Many drivers limit current well below the ideal V/R stall estimate.

Why does I ≈ P/V not match my clamp meter?

Power ratings may be mechanical output, controller efficiency varies, and current can be pulsed. Also, voltage sag under load changes the math.

Do I need Kv or Kt?

For torque-based estimates you need Kt. If you only have Kv (rpm/V), the tool can approximate Kt using the standard conversion.

Tool Info

Last updated:

Updates may include unit support, edge-case handling, and UI improvements.