Hull Speed Calculator
Hull speed is the theoretical maximum efficient speed of a displacement hull. It is calculated as 1.34 times the square root of the waterline length in feet. At hull speed, a displacement boat's bow wave matches its hull length, and pushing through requires dramatically more power. Enter your waterline length in feet or metres to find your boat's hull speed in knots and mph.
Hull speed formula
Vs = 1.34 × √LWL
Where Vs is hull speed in knots and LWL is the waterline length in feet. The constant 1.34 comes from wave speed theory: the speed of a wave (in knots) equals approximately 1.34 times the square root of its wavelength in feet.
Typical hull speeds by boat size
| LWL (ft) | LWL (m) | Hull Speed (kn) |
|---|---|---|
| 20 | 6.1 | 5.99 |
| 25 | 7.6 | 6.70 |
| 30 | 9.1 | 7.34 |
| 36 | 11.0 | 8.04 |
| 40 | 12.2 | 8.47 |
| 50 | 15.2 | 9.47 |
| 65 | 19.8 | 10.80 |
Hull speed calculator: frequently asked questions
What is hull speed?
Hull speed is the theoretical maximum efficient speed of a displacement hull (a boat that sits in the water rather than planing on top). At hull speed, the boat sits in its own bow wave and requires exponentially more power to go faster. It is not an absolute limit but a practical efficiency threshold.
What is the hull speed formula?
Hull speed (Vs) in knots equals 1.34 multiplied by the square root of the waterline length (LWL) in feet. For example, a 36-foot waterline gives Vs = 1.34 * sqrt(36) = 1.34 * 6 = 8.04 knots.
Why does waterline length affect hull speed?
A longer waterline produces longer bow waves. The speed of a wave is proportional to the square root of its length. When a boat reaches hull speed, its bow and stern waves synchronise, and the boat effectively sits in a trough. A longer hull creates longer, faster waves, raising the hull speed.
Does hull speed apply to planing boats?
No. Planing hulls break free of their bow wave at speed and rise onto the surface of the water. Hull speed is only relevant to displacement hulls such as sailboats, trawlers, and full-keel cruising boats. Performance sailboats and powerboats can exceed hull speed by planing.
What is the constant 1.34 in the hull speed formula?
The constant 1.34 is an empirical value derived from the relationship between wave speed and wavelength in seawater. Some naval architects use 1.34 for heavy displacement hulls and up to 1.5 for lighter semi-displacement designs. This calculator uses 1.34, the widely accepted standard for displacement hulls.
Official sources
- Larsson, L. and Eliasson, R. (2000). Principles of Yacht Design. International Marine/Ragged Mountain Press. Standard naval architecture reference for the 1.34 constant.
- NOAA National Ocean Service: What is a nautical mile?
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.