Skip to content
Calculator Tools
Marine & Boating Calculators

Propeller Slip Calculator

Propeller slip percentage from pitch, engine RPM, gear ratio and actual boat speed.

Enter values

Results update as you type.

Result

Propeller slip

-27.31%

Theoretical speed at 17.3 knots assumes the prop advances its full pitch with every turn — real propellers never do.

Theoretical speed
17.28 knots
Actual speed
22 knots
Propeller RPM
1,500
Assessment
Negative slip — check the pitch or speed figures
Speed per 100 RPM
0.733 knots

About the Propeller Slip Calculator

Propeller slip percentage from pitch, engine RPM, gear ratio and actual boat speed.

Also known as: prop slip calculator, theoretical boat speed, propeller pitch calculator.

How to use this calculator

  1. Enter propeller pitch, engine rpm, gear ratio, actual boat speed.
  2. The result updates instantly as you type — press Calculate (or Enter) at any time.
  3. Review the breakdown shown under the main result.
  4. Use Copy result or Share to save the answer or send a link with your inputs.

Formula

slip % = (theoretical speed − actual speed) ÷ theoretical speed × 100

Worked example

Using the values pre-filled in the calculator above:

  • Propeller pitch = 14 inches
  • Engine RPM = 3,000
  • Gear ratio = 2
  • Actual boat speed = 22 knots

the calculator returns:

  • Propeller slip: -27.31%
  • Theoretical speed: 17.28 knots
  • Actual speed: 22 knots
  • Propeller RPM: 1,500