RC Motor KV to RPM Calculator
Calculate RC motor RPM from KV rating and battery voltage (RPM = KV × volts) for any LiPo cell count.
Returns no-load RPM and prop size recommendations.
The KV rating of a brushless motor is the most important specification for matching motors to batteries and propellers in RC vehicles. KV stands for “RPM per Volt” (the K is from the SI prefix kilo, and V is voltage).
RPM Formula
RPM (no load) = KV × Battery Voltage
Under load (with a propeller or wheels), actual RPM is typically 70–85% of the no-load value due to back-EMF and mechanical resistance.
RPM (loaded) = KV × Voltage × Load Factor
| Application | Load Factor |
|---|---|
| RC Plane (efficient prop) | 0.80–0.85 |
| RC Plane (high pitch prop) | 0.70–0.80 |
| Multirotor/Drone | 0.75–0.85 |
| RC Car (on road) | 0.85–0.90 |
| RC Car (off road) | 0.75–0.85 |
LiPo Battery Voltage Reference
| Cell Count | Nominal Voltage | Full Charge |
|---|---|---|
| 2S | 7.4V | 8.4V |
| 3S | 11.1V | 12.6V |
| 4S | 14.8V | 16.8V |
| 6S | 22.2V | 25.2V |
KV Ranges by Application
| Application | Typical KV | Why |
|---|---|---|
| Large plane (slow flyer) | 400–900 | Large props, high torque |
| Sport plane | 900–1400 | Medium props, good speed |
| Racing plane/jet | 1400–2500 | Small props, very fast |
| FPV racing drone | 1700–2600 | 5" props, high thrust |
| Photography drone | 300–900 | Large props, stability |
| RC car (street) | 3000–5000+ | Small pinion, high RPM |
| RC car (crawler) | 1200–2000 | Low speed, high torque |
Worked Example
A 1400 KV motor on a 3S LiPo (11.1V nominal):
- No-load RPM = 1400 × 11.1 = 15,540 RPM
- Loaded RPM (sport plane) = 1400 × 11.1 × 0.82 = 12,743 RPM
- At full charge (12.6V): 1400 × 12.6 × 0.82 = 14,467 RPM
Prop Speed (tip speed)
Propeller tip speed should stay below Mach 0.7 (~540 mph / 870 km/h) to avoid efficiency loss and excessive noise:
Tip Speed (mph) = π × Prop Diameter (in) × RPM / (12 × 5280 / 60)
For a 10" prop at 12,743 RPM: Tip Speed = π × 10 × 12,743 / 1056 = 379 mph (safe, well under Mach 0.7)
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
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