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 six 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 (on-road) | 0.87 | 0.85–0.90, hard surface, low rolling loss |
| RC Car (off road/crawler) | 0.80 | 0.75–0.85 |
An on-road car sits at the top of that range because tarmac costs far less than dirt. A crawler on rocks sits at the bottom, and a crawler that is actually stalled against an obstacle is drawing full current at no RPM at all, which is a condition no load factor describes.
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 |
| 5S | 18.5V | 21.0V |
| 6S | 22.2V | 25.2V |
Nominal is 3.7V per cell and full charge is 4.2V. The dropdown offers all five counts above, so the 5S row is here rather than left out as an oddity.
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 (about 533 mph, taking Mach 1 as 761 mph at sea level) to avoid efficiency loss and excessive noise:
Tip Speed (mph) = π × Prop Diameter (in) × RPM / (12 × 5280 / 60)
The calculator checks this at the full-charge RPM, not the nominal one, because that is the fastest the prop ever turns and it happens on every flight in the first minute off the pack. Checking the nominal figure would pass setups that are over the limit whenever the battery is fresh.
Same 1400 KV motor on 3S with a 10" prop: at 12.6 V full charge and the 0.82 efficient-plane factor, that is 14,465 RPM.
Tip Speed = π × 10 × 14,465 / 1056 = 430 mph, or Mach 0.57. Comfortable.
That same 10" prop hits the limit around 17,900 RPM, which the same motor reaches on 6S. Tip speed is why a low-KV motor swinging a big prop is not just a slower version of a high-KV motor on a small one: the big prop runs out of tip speed first, and the noise arrives well before the failure does.
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.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.