RC Prop Power Calculator

Calculator

Prop Diameter

Inches

Prop Pitch

Inches

Blade Count

Use 2 for normal two blade props.

Manual RPM

Leave blank to estimate from KV.

Motor KV

Used only when manual RPM is blank.

Battery Voltage

Volts under load.

Throttle

Percent.

Motor Load Factor

Typical range is 0.75 to 0.90.

Air Density

kg/m³. Sea level is about 1.225.

Power Coefficient Cp

Use test data when known.

Thrust Coefficient Ct

Static estimate coefficient.

Prop Efficiency

Percent.

Drive Efficiency

Motor and ESC combined percent.

Flight Speed

m/s. Use 0 for static estimate.

Measured Current

Optional amps from wattmeter.

ESC Current Limit

Amps.

Battery Capacity

mAh.

Battery C Rating

Continuous rating.

Formula Used

The calculator uses common propeller coefficient relations. These are estimates. Real propeller test data gives better precision.

Diameter in meters: D = diameter inches × 0.0254
Pitch in meters: pitch = pitch inches × 0.0254
Revolutions per second: n = RPM ÷ 60
Blade factor: blade factor = blade count ÷ 2
Shaft power: P = Cp × blade factor × ρ × n³ × D⁵
Torque: Q = P ÷ 2πn
Static thrust: F = Ct × blade factor × ρ × n² × D⁴
Pitch speed: pitch speed = pitch inches × RPM ÷ 1056
Estimated current: I = P ÷ voltage ÷ drive efficiency
Tip speed: tip speed = π × D × n

How To Use This Calculator

Enter the propeller diameter, pitch, and blade count.
Enter measured RPM, or leave RPM blank and enter motor KV.
Add battery voltage, throttle, and motor load factor.
Enter air density and coefficient values for your propeller.
Use measured current when you have wattmeter data.
Compare current with ESC and battery limits.
Press Calculate to view the result above the form.
Use CSV or PDF download for record keeping.

Example Data Table

Diameter	Pitch	RPM	Voltage	Cp	Ct	Use Case
8 in	4 in	10500	11.1 V	0.040	0.090	Light sport model
10 in	6 in	9000	11.1 V	0.045	0.100	Trainer setup
12 in	6 in	7200	14.8 V	0.050	0.110	Slow climb setup
13 in	8 in	6500	22.2 V	0.055	0.115	Larger electric aircraft

Understanding RC Prop Power

An RC propeller looks simple, yet it controls much of the aircraft load. Diameter sets the swept area. Pitch sets the theoretical travel per turn. RPM sets how often the blade works. Together, these values decide the power needed from the motor.

Why Power Matters

Power is not only a speed number. It shows how hard the propeller loads the shaft. A small increase in RPM can create a large power change, because propeller power rises with the cube of revolutions per second. Diameter is even more sensitive. It is raised to the fifth power in the standard coefficient method. This is why a slightly larger prop can overheat a motor fast.

Thrust And Pitch Speed

Static thrust estimates the pulling force while the model is not moving. It helps compare takeoff setups. Pitch speed estimates the ideal airspeed from pitch and RPM. Real speed is lower because blades slip in air. A high pitch speed does not always mean better climb. A low pitch, large diameter prop may climb better at slower flight speed.

Battery And Motor Checks

The calculator estimates shaft power first. Then it estimates electrical input from voltage and drive efficiency. Current is useful for checking ESC, battery, and motor limits. If you enter measured current, the tool can compare it with the calculated shaft demand. This helps find poor matching or unrealistic coefficients.

Using Coefficients Carefully

The power coefficient and thrust coefficient are approximations. Real values change with blade shape, airfoil, Reynolds number, and forward speed. Use maker test data when available. Use conservative values for unknown props. Treat results as planning data, not a final safety guarantee.

Better Setup Decisions

Try several diameters, pitches, and RPM values. Watch shaft power, current, torque, and thrust together. A setup with balanced numbers is usually better than one extreme result. Keep electrical load below rated limits. Leave cooling margin. Test on a wattmeter before flying. Use this calculator to narrow choices, document results, and compare setups clearly before field testing. Record each test with the same battery charge and weather. Small testing habits make comparisons more reliable and expose risky combinations early. Recheck prop balance and mounting carefully before every high power run.

FAQs

1. What does RC prop power mean?

It is the estimated shaft power needed to spin a propeller at a chosen RPM. It helps check whether the motor, ESC, and battery can handle the propeller load safely.

2. Why does diameter affect power so much?

Propeller power changes with diameter raised to the fifth power. A small diameter increase can greatly increase load. Always retest current after changing prop size.

3. Should I use measured RPM or motor KV?

Measured RPM is better. KV estimates are useful for planning, but real RPM changes with prop load, battery sag, motor resistance, and ESC timing.

4. What is a good power coefficient?

It depends on the propeller. Many rough estimates use values near 0.035 to 0.070. Use manufacturer test data when available for better results.

5. What is static thrust?

Static thrust is the pulling force when the model is not moving. It helps compare takeoff and hover setups, but it does not fully describe flight performance.

6. What is pitch speed?

Pitch speed is theoretical speed from pitch and RPM. Real aircraft speed is lower because air slips around the propeller and drag rises during flight.

7. Why is tip Mach important?

High propeller tip Mach can create noise, drag, vibration, and stress. Many builders avoid very high values to protect efficiency and propeller safety.

8. Can this replace wattmeter testing?

No. This calculator is for planning and comparison. Always verify current, voltage, RPM, and temperature with real bench testing before flying.