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.
Specialist tool for RC Drones1 documented formula11 real workflowsPrivate in your browser
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A quick decision brief for this specific tool
Inputs that matter
Motor KV Rating, Battery Voltage, Propeller Diameter, Motor Efficiency
Output to expect
Motor KV Calculator
How it works
1 documented formula across 1 calculation mode
- Keep 4 bounded inputs within the limits shown beside the fields.
- Confirm that every value uses the unit and time basis shown before comparing scenarios.
- Change one input at a time to see which assumption materially changes the result.
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Reference & details
How it works
Updated July 2026
How it works
Updated July 2026KV 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) / 1056Power 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
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.