Hull Speed Calculator

Theoretical hull speed of a displacement boat from its waterline length.

Enter values

Result

Hull speed

7.281 knots

In km/h: 13.49
In mph: 8.38
Waterline length: 29.53 ft
Speed–length ratio: 1.34
Semi-displacement potential (S/L 1.6): 8.69 knots
Day’s run at hull speed: 175 nm

About the Hull Speed Calculator

A displacement hull makes a wave as long as itself, and once it is trapped in that wave it cannot go much faster without planing. Hull speed in knots is roughly 1.34 times the square root of the waterline length in feet — a limit that has shaped boat design for centuries.

Also known as: displacement speed, boat hull speed, waterline speed calculator, maximum boat speed.

How to use this calculator

Enter waterline length, unit.
The result updates instantly as you type — press Calculate (or Enter) at any time.
Review the breakdown shown under the main result.
Use Copy result or Share to save the answer or send a link with your inputs.

Formula

hull speed (knots) = 1.34 × √(waterline length in feet)

Worked example

Using the values pre-filled in the calculator above:

Waterline length = 9
Unit: Metres

the calculator returns:

Hull speed: 7.281 knots
In km/h: 13.49
In mph: 8.38
Waterline length: 29.53 ft

Frequently asked questions

Can a boat exceed hull speed?

A planing hull can, with enough power. A heavy displacement hull effectively cannot without an enormous power increase.