Advanced Propeller Sizing Calculator

Size propellers using power, rpm, speed, and efficiency. Review thrust, pitch, and tip-speed checks instantly. Make early engineering choices with clearer performance insight today.

Calculated Propeller Recommendation

Detailed Output

Diameter Sensitivity vs Shaft RPM

This graph compares the power-based diameter, thrust-based diameter, and final recommended diameter across a practical RPM range.

Calculator Inputs

Enter your design point values below. Results appear above this form after calculation.

Fluid changes density and speed assumptions.
Used for air density and speed of sound.
Enter delivered shaft power.
Horsepower uses mechanical hp.
Use propeller shaft speed, not engine speed.
Use cruise or design-point speed.
Used for pitch and advance ratio.
Enter a realistic design estimate.
Used for pitch estimation from speed.
Affects automatic coefficient defaults.
Choose the expected duty emphasis.
Override automatic fluid density if needed.
Only used when override is enabled.
Use your own nondimensional coefficients.
Used in P = CPρn³D⁵.
Used in T = CTρn²D⁴.
Automatic coefficients: CP 0.070, CT 0.090

Example Data Table

These sample rows use the same estimation method as the calculator.

Scenario Fluid Power RPM Speed Efficiency Slip Estimated Diameter Estimated Pitch Estimated Thrust
Homebuilt aircraft Air 12 kW 2600 45 m/s 82% 10% 1.064 m 1.154 m 218.7 N
Survey UAV Air 4.5 kW 4800 28 m/s 75% 12% 0.630 m 0.398 m 120.5 N
STOL concept Air 22 kW 2200 32 m/s 80% 15% 1.315 m 1.027 m 550.0 N

Formula Used

1) Advance ratio

J = V / (nD)

V is forward speed, n is revolutions per second, and D is diameter.

2) Power-based diameter estimate

CP = P / (ρn3D5)

Rearranged: D = [ P / (CPρn3) ]1/5

3) Thrust-based diameter estimate

CT = T / (ρn2D4)

Rearranged: D = [ T / (CTρn2) ]1/4

4) Thrust estimate from power and efficiency

T ≈ ηP / V

This links useful propulsive power to forward speed at the selected design point.

5) Pitch estimate from speed and slip

Pitch ≈ V / [ n(1 − slip) ]

Higher slip requires more theoretical pitch for the same actual speed.

6) Disk loading and tip-speed check

Disk loading = T / (πD²/4)

Tip speed = πDn

For air: Mtip = √[(πDn)² + V²] / a

This calculator is intended for preliminary sizing and trade studies. Final propeller design still needs blade geometry, structural, noise, and detailed efficiency analysis.

How to Use This Calculator

  1. Choose the working fluid first.
  2. Enter altitude when the propeller operates in air.
  3. Type the shaft power delivered to the propeller.
  4. Enter propeller shaft RPM at the design point.
  5. Provide target forward speed and its unit.
  6. Set realistic efficiency and slip assumptions.
  7. Select blade count and duty bias.
  8. Override density or coefficients only if you know them.
  9. Press calculate to show results above the form.
  10. Review diameter, pitch, thrust, and warning notes.
  11. Check the RPM sensitivity plot before final choices.
  12. Download CSV or PDF for reporting or comparison.

Frequently Asked Questions

1) What does this calculator size first?

It estimates propeller diameter and pitch at one design point. It also reports thrust, torque, disk loading, advance ratio, and tip-speed checks to support early selection work.

2) Is this for air or water propellers?

It can estimate both. The fluid selector changes density assumptions, while altitude affects only air calculations. Water cases skip the air tip Mach result and keep the tip-speed output.

3) Why are CP and CT included?

These nondimensional coefficients let the calculator connect power, thrust, density, RPM, and diameter. They are useful during preliminary sizing before detailed blade geometry is available.

4) Can I use my own test data?

Yes. Enable manual coefficient override and enter your known CP and CT values. You can also override density when your operating condition differs from the standard assumption.

5) What does slip mean here?

Slip is the gap between theoretical forward travel per revolution and the actual travel achieved. The calculator uses it only to estimate pitch from speed and shaft rotation.

6) Why do I get two diameter estimates?

One comes from the power relation and the other comes from the thrust relation. The final recommendation averages both so you can compare the balance between absorbed power and delivered thrust.

7) What should I do with warning messages?

Treat them as design prompts. Adjust RPM, diameter, pitch, efficiency, or coefficients, then recalculate. Warning notes help identify combinations that may deserve closer aerodynamic or mechanical review.

8) Is this enough for final manufacturing?

No. Final manufacturing needs blade section selection, twist, chord distribution, structural checks, noise limits, and detailed performance testing or higher-order modeling.


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Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.