Propeller Thrust Calculator
Static thrust in N, lbf and kgf from propeller diameter, pitch, RPM and blades in air or water, plus ideal power at your airspeed from momentum theory. How it works
Use the Propeller Thrust Calculator
About the Propeller Thrust Calculator
A 10 × 4.5 in two-blade propeller at 10,000 RPM at sea level makes 12.18 N of static thrust, which is 2.74 lbf or 1.24 kgf. The propeller thrust calculator uses T = Ct × ρ × n² × D⁴ with an empirical thrust coefficient (Ct = 0.086 for this propeller), and it adds the ideal power from momentum theory: 120.65 W at zero airspeed, or an estimated 185.6 W (0.249 hp) at the shaft with an assumed 65% propeller efficiency.
Static thrust of a 10 × 4.5 in two-blade propeller by RPM
| RPM | Thrust (N) | Thrust (lbf) | Thrust (kgf) | Tip Mach | Ideal power (W) |
|---|---|---|---|---|---|
| 3,000 | 1.10 | 0.25 | 0.11 | 0.12 | 3.3 |
| 5,000 | 3.05 | 0.68 | 0.31 | 0.20 | 15.1 |
| 7,500 | 6.85 | 1.54 | 0.70 | 0.29 | 50.9 |
| 10,000 | 12.18 | 2.74 | 1.24 | 0.39 | 120.7 |
| 12,000 | 17.54 | 3.94 | 1.79 | 0.47 | 208.5 |
| 15,000 | 27.41 | 6.16 | 2.79 | 0.59 | 407.2 |
Sea level, 15 °C, airspeed 0. Thrust scales with RPM squared: doubling the speed multiplies thrust by four. Ct = 0.086 for this propeller.
Air density and thrust by altitude at 15 °C, 10,000 RPM
| Altitude | Air density (kg/m³) | Thrust (N) |
|---|---|---|
| 0 m | 1.2250 | 12.18 |
| 500 m | 1.1541 | 11.48 |
| 1,000 m | 1.0866 | 10.80 |
| 2,000 m | 0.9611 | 9.56 |
| 3,000 m | 0.8476 | 8.43 |
| 5,000 m | 0.6531 | 6.49 |
ISA pressure for the altitude with the air temperature you enter. The tool accepts 0 to 11,000 m (the troposphere). Thrust is proportional to air density.
Airspeed changes the ideal power, not the thrust
| Airspeed | Thrust (N) | Induced velocity (m/s) | Ideal power (W) | Thrust per watt (N/W) |
|---|---|---|---|---|
| 0 km/h | 12.18 | 9.91 | 120.7 | 0.1010 |
| 20 km/h | 12.18 | 7.51 | 159.1 | 0.0765 |
| 40 km/h | 12.18 | 5.80 | 206.0 | 0.0591 |
| 80 km/h | 12.18 | 3.77 | 316.6 | 0.0385 |
This model has no advance-ratio thrust curve, so the thrust stays at its static value at every airspeed.
How to use this tool
- Choose metric (cm, km/h, m, °C) or imperial (in, mph, ft, °F). Switching converts the numbers you already typed, so the propeller stays the same.
- Enter the diameter, pitch, RPM, airspeed (0 for static) and the number of blades, from 2 to 6. A prop labeled 10x4.5, or 1045 on many drone props, is 10 in diameter and 4.5 in pitch.
- For air, enter the altitude and air temperature. Choose fresh or salt water to use a water density instead.
- Optionally replace the thrust coefficient constant (0.105) with one from a maker’s test, and the assumed efficiency (65%) used for the shaft-power estimate.
- Read the static thrust, the ideal power at your airspeed, the shaft-power estimate, the tip speed and Mach number, and the disk loading. Open the calculation breakdown for Ct, density and the advance ratio.
Frequently asked questions
- How much thrust does a 10 inch propeller make at 10,000 RPM?
- A 10 × 4.5 in two-blade propeller makes 12.18 N, or 2.74 lbf, at sea level and 15 °C. A 9 × 6 in propeller at 12,000 RPM makes 12.70 N. In this model thrust grows with the square of RPM and about the 3.75th power of diameter, so a small change in diameter matters far more than a similar change in pitch.
- How do I convert thrust from newtons to kg or pounds?
- Divide newtons by 9.80665 for kilograms-force and by 4.44822 for pounds-force: 12.18 N is 1.24 kgf and 2.74 lbf. A kgf is a force, not a mass, so 1.24 kgf means the thrust could hold up about 1.24 kg against gravity.
- Does thrust change with airspeed?
- Not in this model. The thrust is the static value at every airspeed, because the tool has no advance-ratio thrust curve. Airspeed changes the induced velocity and the ideal power: for the default propeller the ideal power rises from 120.7 W at 0 km/h to 316.6 W at 80 km/h while the thrust stays 12.18 N. A real propeller loses thrust as forward speed rises, which this tool does not show.
- How does altitude or temperature change the thrust?
- Through air density. The tool takes ISA pressure for the altitude and your air temperature: 1.2250 kg/m³ at sea level and 15 °C, 1.0866 kg/m³ at 1,000 m and 0.6531 kg/m³ at 5,000 m. Thrust follows density, so the default propeller makes 10.80 N at 1,000 m and 6.49 N at 5,000 m. At sea level it makes 13.86 N at −20 °C and 11.03 N at 45 °C. Altitude is limited to 0 to 11,000 m, the troposphere.
- How does the number of blades change the result?
- The coefficient is scaled by the square root of the blades divided by 2, so the default propeller makes 12.18 N with 2 blades, 14.92 N with 3 and 17.23 N with 4. The square-root scaling is part of the tool’s own rule of thumb, so treat the 3- and 4-blade figures as rough.
- Can I use it for a boat propeller?
- Only as a density comparison. Choose fresh water (999.1 kg/m³) or salt water (1025.0 kg/m³) and the tool scales the same air-propeller coefficient by the density: at 1,000 RPM the default propeller gives 99.34 N in fresh water and 101.92 N in salt water, against 0.12 N in air. That is not a boat-propeller prediction. Marine propellers have their own coefficients, and cavitation, slip and the hull are not modeled.
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