DC Motor Speed / Torque
Armature & constants
Enter supply, armature resistance, and either current or back-EMF; speed, torque and power appear live.
Motor performance
How to use this calculator
A DC motor's armature obeys V = Eb + Ia·Ra, where the back-EMF Eb = Ka·ω opposes the supply. Enter the supply voltage, armature resistance, and either the armature current (which gives you Eb) or Eb (which gives you current), plus the back-EMF constant Ka, and the calculator derives speed, torque and power live. If you provide a torque constant Kt, it's used for torque; otherwise Kt = Ka (the SI relationship).
What it means in a real circuit
For a 12 V supply, 1 Ω armature, 10 A current and Ka = 0.01 V·s/rad, the back-EMF is 12 − 10 = 2 V, giving ω = 200 rad/s (≈ 1910 rpm) and torque = Kt·Ia = 0.01×10 = 0.1 N·m. At no load the current is small and speed is high; as mechanical load increases, current rises, back-EMF falls, and speed drops — that's the natural speed regulation of a DC motor. Use this to estimate speed and torque for a given supply and load current, or to back-calculate what current a load will draw.