Motor Power Calculator
Calculate required motor power from torque and speed, or back-calculate torque from power and speed — with results in kW and HP.
Enter your values
Choose direction, then fill in the fields below.
How this calculator works
Mechanical power at a rotating shaft is torque multiplied by angular velocity:
T is torque in N·m, N is speed in RPM, and P comes out in watts (the calculator displays it in kW and HP). If you're solving for torque instead, the formula is rearranged:
If you enter a mechanical efficiency below 100%, the calculator divides the ideal power (or multiplies the required torque) accordingly, to give the input power a motor must actually supply to overcome losses.
Unit conversion reference
| From | To | Multiply by |
|---|---|---|
| kW | HP (mechanical) | 1.341 |
| HP (mechanical) | kW | 0.7457 |
| N·m | lb·ft | 0.7376 |
Frequently asked questions
Should I size a motor at exactly this calculated power?
No — apply a service factor above the calculated value (commonly 1.15–1.5×) to cover starting loads, duty cycle, and future margin, then select the next standard motor frame size at or above that.
Does this account for starting torque?
No — this is steady-state running power. Starting torque requirements for high-inertia loads should be checked separately against the motor's starting torque curve.