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Motor KV Calculator

Calculate motor KV rating, RPM, and max power from voltage and no-load speed. Size brushless motors for drone and RC aircraft applications.

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Inputs that matter
Motor KV Rating, Battery Voltage, Propeller Diameter, Motor Efficiency
Output to expect
Motor KV Calculator
  • Check the units and required inputs before comparing results.
  • Keep the assumptions with a copied result so you can reproduce the calculation later.
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Reference & details

How it works

KV Definition

KV is RPM per volt at no load. A 2300 KV motor on 11.1V (3S) theoretically spins 25,530 RPM unloaded. Loaded RPM is 80–90% due to prop drag.

KV = RPM_no-load / voltage (V)

Loaded RPM Estimation

Under prop load, RPM drops 10–20% from no-load. Pitch speed = RPM × pitch / 1056 (mph) guides prop selection for target airspeed.

Pitch speed (mph) = RPM × pitch (in) / 1056

Power and Current Relationship

Electrical power in = voltage × current. Mechanical output is 70–85% of input at optimal efficiency point — typically 60–70% throttle.

Pin (W) = V × I; Pout ≈ Pin × efficiency (0.70–0.85)

Updated: July 2026

Example Scenarios

No-load spin on 12.0V measures 27,600 RPM: KV = 27600/12 = 2300. Verify briefly without prop — extended no-load damages some motors.

1750 KV on 4S (16.8V max): loaded ~24k RPM — ideal for 5-inch props. Same size 1200 KV on 6S (25.2V): similar RPM range for 5–6 inch with lower amp draw.

2200 KV on 2S (7.4V), 8×4 prop loaded 14k RPM: pitch speed = 14000×4/1056 ≈ 53 mph theoretical max — adequate for sport plane.

Common Mistakes to Avoid

Selecting KV without considering battery cell count

KV must pair with voltage. A motor chosen for 4S may over-rev dangerously on 6S. Calculate loaded RPM = KV × voltage before buying.

Running no-load motor tests for extended periods

No-load current is low but RPM is maximum — bearings and windings overheat without prop load cooling. Brief tests only.

FAQ

4S: 1600–1900 KV for 5-inch. 6S: 1200–1500 KV. Higher KV spins faster with smaller props; lower KV uses larger props with more torque.

Higher KV increases RPM at same voltage but may require smaller props. Top speed depends on pitch speed (RPM × pitch), not KV alone.

Overshooting RPM exceeds motor and prop mechanical limits. A 2300 KV motor on 6S exceeds most 5-inch prop ratings — use appropriate KV for cell count.

Brief no-load test at partial throttle with current limit, or use manufacturer spec. Some motors should never run no-load — check datasheet.

Lower KV motors have more turns of wire, producing higher torque at lower RPM. Higher KV spins faster with less torque — match to prop size and application.

About Motor KV Calculator

Motor KV defines RPM per volt of no-load speed and drives prop selection with battery voltage. This calculator computes KV from measured RPM and voltage, or predicts RPM and power from KV and cell count.