Calculate brushless motor RPM from Kv and voltage, or solve for motor Kv or required voltage, with LiPo battery presets and optional load estimates.

Kv is a motor speed constant in RPM/V, not kilovolts. Kv ร— voltage estimates ideal no-load mechanical speed. Actual speed depends on load, controller, losses and battery sag.

Operating-speed assumption

100% gives the ideal no-load estimate. Lower values are your assumed fraction of that speed, not motor efficiency. Blank means 100%.

RPM from Kv Rating Formula

RPM = Kv ร— V

Variables:

  • RPM is the RPM from Kv Rating (rotations per minute)
  • Kv is the motor velocity constant, expressed in RPM per volt (not kilovolts)
  • V is the voltage (volts)

To estimate ideal no-load mechanical RPM, multiply Kv in RPM/V by the applied motor voltage. Actual loaded speed is lower or otherwise controller-dependent; the optional speed factor is a user assumption, not efficiency. The reverse modes use no-load RPM. See maxonโ€™s speed-constant explanation.

Voltage and Motor Kv to RPM Conversion Table (RPM = Kv ร— Voltage; Kv in RPM/V)
Voltage (V) Kv (RPM/V) RPM
5.010005000
6.0200012000
7.4230017020
9.010009000
11.1220024420
12.0100012000
12.0140016800
14.8100014800
14.8170025160
18.5100018500
18.5150027750
22.2100022200
22.2150033300
22.2190042180
24.0100024000
24.02506000
36.040014400
37.092034040
44.440017760
48.01507200
* RPM rounded to whole numbers. Assumes no-load RPM and Kv expressed in RPM per volt.

How to Calculate RPM from Kv Rating?

The following steps outline how to calculate the RPM from Kv Rating.

  1. First, determine the Kv rating. 
  2. Next, determine the voltage (volts). 
  3. Next, gather the formula from above: RPM = Kv * V.
  4. Finally, calculate the RPM from Kv Rating.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

Kv rating = 67

voltage (volts) = 80

Ideal no-load RPM = 67 ร— 80 = 5,360 RPM. This arithmetic does not establish a safe motor/controller voltage or mechanical speed. LiPo presets use conventional per-cell voltage assumptions, with full-charge voltage higher than nominal. The rounded series-cell reference is not a battery recommendation; check the equipment limits and battery specification. Conventional values are illustrated in the manufacturer battery-parameter table; storage targets vary by battery.