Propeller Pitch Calculator
Marine propulsion specialist focused on propeller hydrodynamics, waterjets, shafting, and marine propulsion sy...
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Senior Naval Architect & Marine Engineer with 15+ years of experience in offshore engineering, subsea installa...
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Naval Architect and Professional Engineer specializing in high-speed small craft, surface-piercing propellers,...
View ProfileUse our Propeller Pitch calculator to find boat prop pitch, speed, slip, and prop RPM with simple steps and clear results.
| Equation | Solves For | Notes |
|---|---|---|
| P = V × GR × 1056 ÷ (RPM(1−S)) | Pitch (inches) | Speed V in mph |
| P = V × GR × 1215.2 ÷ (RPM(1−S)) | Pitch (inches) | Speed V in knots |
| RPM_prop = RPM_engine ÷ GR | Propeller shaft RPM | After gear reduction |
| V = (RPM÷GR) × P(1−S) ÷ K | Boat speed | K = 1056 (mph) or 1215.2 (knots) |
| S = 1 − (V×GR×K) ÷ (RPM×P) | Propeller slip | From a measured actual speed |
| P = 2πr × tan(β) | Geometric pitch | Blade design, not speed-based sizing |
A Propeller Pitch calculator helps you find the right prop pitch for a boat. It can also find boat speed and prop slip. Our tool uses speed, gear ratio, engine RPM, and slip. You can use it to check a prop setup with ease.
Propeller Pitch Formula
For speed in mph, use:
P = V × GR × 1056 ÷ [RPM × (1 − S)]
For speed in knots, use:
P = V × GR × 1215.2 ÷ [RPM × (1 − S)]
Here, P means pitch in inches. V means boat speed. GR means gear ratio. RPM means engine speed. S means slip as a decimal. Thus, 20% slip means S = 0.20.
The tool also finds prop RPM:
Prop RPM = Engine RPM ÷ Gear Ratio
Pitch is the set travel of a prop in one turn, with no slip. A higher pitch can give more top speed. A lower pitch can give more pull and faster take-off. Boat load, hull form, prop type, and water can change the real result.
How to use online Propeller Pitch calculator
- Pick the Pitch mode.
- Enter your target boat speed.
- Enter the gear ratio and engine RPM.
- Enter the expected prop slip.
- Click Calculate. The tool shows pitch and prop RPM.
You can also use Speed mode. It finds speed from a known pitch. Slip mode finds slip from speed and pitch. Geo mode finds pitch from blade radius and pitch angle.
Example Propeller Pitch calculation
Say your boat has a target speed of 50 mph. The gear ratio is 2. The engine runs at 5,500 RPM. Slip is 20%.
First, turn slip into a decimal:
S = 20 ÷ 100 = 0.20
Now use the pitch formula:
P = 50 × 2 × 1056 ÷ [5,500 × (1 − 0.20)]
P = 105,600 ÷ 4,400
P = 24 inches
Now find prop RPM:
Prop RPM = 5,500 ÷ 2 = 2,750 RPM
So, the result is a 24-inch pitch at 2,750 prop RPM.
How much does 1 pitch change in RPM?
There is no exact RPM change for one inch of pitch. A common guide says one inch can change WOT RPM by about 150 to 200 RPM.
If you add one inch of pitch, RPM may drop by 150 to 200. If you cut one inch, RPM may rise by 150 to 200. The real change can vary with the prop, boat, load, and water.
Always check the engine maker’s WOT RPM range. Mercury notes that the right prop should let the engine run in its rated RPM range.
Final Verdict
A Boat propeller pitch calculator makes prop choice much easier. Enter good test data for a better result. Check the WOT RPM range too. A good prop should help the engine reach its rated RPM. It should also give the speed and pull you need.
FAQs
What is propeller pitch?
Pitch is the set forward travel of a prop in one turn, with no slip.
How to calculate propeller pitch?
Use boat speed, gear ratio, engine RPM, and slip in the formula above.
What does higher pitch do?
A higher pitch can lower engine RPM. It may also raise top speed. Yet, it can reduce take-off power.
What does lower pitch do?
A lower pitch can raise engine RPM. It can also improve pull and take-off.
Can this tool find boat speed?
Yes. Use the Propeller pitch speed calculator mode. Enter pitch, RPM, gear ratio, and slip.
Is propeller pitch the same as prop size?
No. Pitch and diameter are different. Pitch shows forward travel per turn. Diameter shows the size of the prop’s sweep.