Drone Motor Calculator (thrust per motor, power & current from thrust-to-weight)

Understanding the drone motor calculator — concept and principle

Choosing motors for a multicopter starts with how much thrust each must make. This calculator finds the full-throttle thrust per motor from the take-off mass and the thrust-to-weight ratio you want, then estimates shaft power, electrical power and current per motor using momentum theory, so you can pick motors, propellers and speed controllers with margin.

Each motor must lift 700 g at full thrust, drawing about 7.7 A at 14.8 V.

How it is calculated

Full thrust per motor (g) = mass × TWR ÷ number of motors

Hover thrust per motor = mass ÷ number of motors; share used to hover = 100 ÷ TWR %

Ideal power for thrust T (N): P = T^1.5 ÷ √(2 ρ π r²), ρ = 1.225 kg/m³

Shaft power = ideal ÷ figure of merit

Electrical power = shaft ÷ motor and ESC efficiency; current = electrical ÷ battery voltage

r is the propeller radius (diameter in inches × 0.0254 ÷ 2).

The principle

A drone needs spare thrust beyond its weight to climb, manoeuvre and resist wind. The thrust-to-weight ratio sets that spare: at TWR 2, each motor can make twice the thrust it needs to hover. Momentum theory gives the minimum power to produce a given static thrust with a given propeller disc: power grows with thrust to the 1.5 power, so doubling thrust needs about 2.8 times the power. Real propellers and motors are less efficient, which the figure of merit and efficiency inputs account for.

Worked example

Default inputs: 1,400 g, 4 motors, TWR 2, 10-inch props, FM 0.6, 75% efficiency, 14.8 V.

Full thrust per motor = 1,400 × 2 ÷ 4 = 700 g; total = 2,800 g.
Hover thrust per motor = 350 g, which is 50% of full thrust.
T = 0.700 × 9.80665 = 6.86 N; ideal power = 6.86^1.5 ÷ √(2 × 1.225 × π × 0.127²) = 51 W; shaft = 51 ÷ 0.6 = 85 W.
Electrical power = 85 ÷ 0.75 = 113 W per motor.
Current = 113 ÷ 14.8 = 7.7 A per motor; total = 30.7 A at full thrust.

Each point is the calculator re-run with only “Number of motors” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Number of motors	Full-throttle thrust per motor (g)
1	2,800
2	1,400
3	933
4	700
5	560
6	467
8	350

How to read the result

Choose motors whose rated thrust with your propeller reaches at least the full-thrust figure, and speed controllers rated comfortably above the current per motor. The battery must deliver the total current; check its continuous discharge rating. Many builders aim for a TWR of about 2 for stable camera drones, and higher for agile flying, but your needs may differ.

Common mistakes

Forgetting payload and battery when entering mass.
Sizing ESCs exactly at the calculated current with no margin.
Ignoring that thrust tables depend on the exact propeller and voltage.
Using the same estimate at high altitude, where thin air needs more power.

Keep in mind: Momentum theory gives a lower bound on power. Confirm with the motor maker's thrust tables and follow safe building and flying practice.

Frequently asked questions

What thrust-to-weight ratio should I aim for?

Around 2 is a common starting point for general-purpose drones; racing drones use much more.

Why does power rise faster than thrust?

Ideal power scales with thrust to the 1.5 power.

How much margin should an ESC have?

Pick a continuous rating comfortably above the calculated current; the maker's guidance is best.

Sources: L. Bauersfeld and D. Scaramuzza, "Range, Endurance, and Optimal Speed Estimates for Multicopters" (arXiv:2109.04741) · U.S. Standard Atmosphere, 1976 (sea-level density 1.225 kg/m³)

Checked 9 Nov 2026. L. Bauersfeld and D. Scaramuzza, “Range, Endurance, and Optimal Speed Estimates for Multicopters” (arXiv:2109.04741): momentum-theory hover power, Eq. 5, propeller figure of merit 0.5–0.7, motor efficiency 0.75 (70–85%); sea-level density 1.225 kg/m³ (U.S. Standard Atmosphere, 1976); g = 9.80665 m/s².

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