Motor Kv Calculator

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Enter the motor's no-load speed at the given voltage.
Voltage at which the RPM was measured.

Motor Kv indicates how many revolutions per minute a motor spins per volt without any load applied. Enter the measured no-load RPM and voltage to instantly determine Kv (RPM/V). Useful for matching controllers, choosing gearing, and estimating no-load speed in electric vehicle projects.

How Motor Kv is calculated

Kv = No-load RPM ÷ Voltage
Higher Kv means higher speed per volt, but usually lower torque.

Where Kv is important

  • BLDC hub motors
  • EV conversion motors
  • RC brushless motors
  • Electric bikes and scooters

Important notes

Kv is a no-load constant and does not include load torque and efficiency losses. Large load and gearing will reduce the actual working RPM significantly.

Frequently Asked Questions

Q: Is Kv torque?
No, Kv is speed per volt. Torque is related by Kt which is the inverse of Kv (in SI units).
Q: Does Kv change under load?
Kv is a constant but measured RPM under load will be lower due to resistance and efficiency losses.
Q: Can I reverse-calculate Kv from datasheet RPM?
Yes, no-load RPM and voltage always gives Kv (RPM ÷ Volt).
Q: Does higher Kv mean more speed?
Yes, higher Kv spins faster per volt, but generally reduces torque output.
Q: Can I convert Kv to Kt?
Yes, Kt ≈ 9.549 / Kv (SI approximation) for brushless motors.