What pitch is
Pitch is the distance a propeller would advance in one revolution through a solid medium — a 6-inch-pitch prop tries to move 6 inches per turn.
Pitch speed
Pitch speed (mph) = Propeller RPM × Pitch (in) / 1056. A 12,000 RPM × 6 in prop yields ≈ 68.2 mph. This is the theoretical ceiling of propeller speed.
Why real speed is lower
Propellers never advance their full pitch — slip, airframe or hull drag, and load cut the real figure, sometimes by 20–40%.
Where it is used
The Pitch Speed Calculator runs the formula; airplanes use RC Airplane Speed, boats RC Boat Speed — all stated as theoretical.