Propeller Pitch Calculator

About the Propeller Pitch Calculator

Propeller pitch is the theoretical distance a propeller would advance in one revolution if there were no slip — like a screw threading into wood. A 12×6 propeller has 12 inches diameter and 6 inches pitch, meaning it theoretically advances 6 inches per revolution.

This calculator computes the theoretical pitch speed (MPH, knots, m/s), tip speed and Mach number, pitch angle at 75% radius, and advance ratio. Tip Mach number is critical — when the blade tips approach Mach 0.85-0.9, compressibility effects cause dramatic efficiency loss and noise.

Preset buttons cover RC model aircraft (2-blade 12×6), multirotors (10×4.5), full-scale Cessna (75×56), and boat propellers. The calculator handles both inch and millimeter inputs. A pitch selection guide helps choose the right pitch for hovering vs speed applications.

Whether you are selecting a propeller for a drone, tuning an RC racing plane, or analyzing a Cessna 172's constant-speed prop, it gives the key performance parameters.

When This Page Helps

Propeller pitch needs to be checked against both the speed you want and the speed the blade tips are already carrying. Pitch speed, tip Mach, and advance ratio together show whether a prop is likely to be efficient, noisy, or simply mismatched.

How to Use the Inputs

1. Select units (inches or millimeters).
2. Enter the propeller diameter and pitch.
3. Enter the RPM and forward airspeed (0 for static).
4. Enter the number of blades.
5. Read the pitch speed, tip Mach, pitch angle, and advance ratio.
6. Check that tip Mach is below 0.85 for efficient operation.

Example Calculation

Tips & Best Practices

• For multirotors, keep pitch at 40-60% of diameter for good hovering efficiency.
• Increasing RPM increases both pitch speed and tip speed — watch the Mach number.
• Wood props are lighter but flex more than carbon fiber at high RPM.
• For boats, typical slip is 20-40% due to the denser medium (water vs air).
• Constant-speed props adjust pitch in flight to maintain optimal RPM across speed ranges.

Pitch, Speed, and Slip

Pitch speed is the idealized forward speed implied by the geometry of the propeller. Real vehicles move slower than that because the prop always has some slip. Looking at pitch speed together with actual operating speed helps show how much of the blade geometry is being turned into useful advance.

Tip Mach and Efficiency

As blade tips move closer to transonic speed, compressibility effects begin to hurt efficiency and increase noise. That is why a prop can look fine by pitch ratio alone but still be a poor choice once RPM and diameter are included.

Practical Selection

The best prop is not just the one with the biggest pitch or diameter. Matching propeller geometry to the operating point is what usually matters most for drones, RC aircraft, boats, and light aircraft.

Frequently Asked Questions

• What is the difference between pitch and actual advance?

  Pitch is the theoretical advance per revolution. Actual advance is less due to slip — typically 10-30% for aircraft props and 20-40% for boat props. Efficiency = actual advance / pitch.

• How do I choose between high and low pitch?

  Low pitch (like low gear): more thrust, less speed — good for hovering, climbing, heavy loads. High pitch (like high gear): less thrust, more speed — good for cruise, racing.

• Why does tip speed matter?

  When blade tips approach the speed of sound (Mach 0.85+), shock waves form, dramatically increasing drag and noise while reducing thrust. Keep tip Mach below 0.85.

• What is advance ratio?

  J = V/(nD) where V is airspeed, n is rev/sec, D is diameter. It determines the operating point on the propeller efficiency curve. Peak efficiency is typically at J = 0.5-0.9.

• Is a bigger prop always better?

  Larger diameter increases disk area and theoretical efficiency (momentum theory), but also increases tip speed, weight, and ground clearance requirements. The optimum balances these factors.

• What does P/D ratio tell me?

  P/D ratio compares pitch to diameter. Low P/D (0.3-0.5) = high thrust, low speed (tugboats, copters). High P/D (0.8-1.2) = low thrust, high speed (fast boats, cruise aircraft).