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
The dropdown above offers five vehicle types, and these are the factors it applies:
| Option in the dropdown | Load factor used | Published range |
|---|---|---|
| RC Plane (efficient) | 0.82 | 0.80–0.85 |
| RC Plane (sport/fast) | 0.75 | 0.70–0.80, higher pitch costs RPM |
| FPV Racing Drone | 0.80 | 0.75–0.85 |
| Photography Drone | 0.82 | 0.75–0.85, larger and gentler props |
| RC Car (off road/crawler) | 0.80 | 0.75–0.85 |
An on-road RC car sits higher still, around 0.85 to 0.90, because a hard surface costs far less than dirt. There is no dropdown entry for it: pick the off-road option and add roughly 8% to the result, or treat the no-load figure as your ceiling.
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), flying a plane on an efficient prop:
- No-load RPM = 1400 × 11.1 = 15,540 RPM
- Loaded RPM = 1400 × 11.1 × 0.82 = 12,743 RPM
- At full charge (12.6V): 1400 × 12.6 × 0.82 = 14,465 RPM
Pick “RC Plane (sport/fast)” instead and the same motor gives 11,655 RPM, because the coarser prop loads it harder. That gap of about 1,100 RPM is the whole reason the vehicle type is an input rather than a fixed constant.
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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