Calculate electric brushless motor thrust, RPM under load, power draw (Watts), and efficiency (grams per Watt).
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The Motor Thrust Calculator determines the thrust, electrical wattage, and mechanical efficiency (grams of thrust per Watt) of brushless electric motors used in drones, RC planes, and robotics. It balances motor KV ratings, battery voltage (LiPo cell count), and propeller load.
\eta_{\text{thrust}} = \frac{\text{Thrust (grams)}}{P_{\text{electrical}} (\text{Watts})} \quad ; \quad P = V \times IGrams per Watt (g/W) measures propulsion efficiency. High-efficiency endurance setups achieve 8–12 g/W, while high-speed racing setups operate at 2.5–4.5 g/W.
Scenario: A motor spinning a 9x4.5 prop at 9,000 RPM drawing 150 Watts and producing 900 grams of thrust.
Thrust: 900 grams.
Power: 150 Watts.
Efficiency: 900 / 150 = 6.00 grams per Watt.
KV is the velocity constant of a brushless motor. It denotes the theoretical RPM the motor will spin per 1 volt of applied electric potential with zero load (e.g. 1000KV on 10V = 10,000 RPM).
For long-range aerial photography drones, 8 to 12 g/W is excellent. For sport RC aircraft, 5 to 7 g/W is standard. For racing quads operating near peak RPM, 2.5 to 4 g/W is normal.
Aerodynamic resistance creates torque load. Under load, a quality brushless motor typically operates at 75% to 85% of its theoretical no-load (KV × Volts) speed.
Higher cell counts (e.g. 6S vs 4S) provide higher voltage, allowing the motor to produce identical power at lower amperage, reducing resistive heat loss (I²R) in wires and ESCs.
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