Hull Speed Calculator
Enter your boat's waterline length to find its theoretical hull speed — the natural speed limit of a displacement hull.
How hull speed is calculated
Theoretical hull speed uses the classic formula Hull speed (kn) = 1.34 × √LWL(ft). It approximates the speed at which a displacement hull's own bow and stern waves have a wavelength equal to the waterline — the point where pushing faster requires disproportionately more power.
It is a guideline, not a hard wall: light, easily-driven and planing hulls can exceed it, while heavy cruisers rarely reach it under sail. For metric input, multiply metres by 3.281 to get feet first.
Why it matters
Hull speed sets realistic passage-planning expectations and helps compare boats — longer waterlines mean higher potential speed, which is why waterline length matters more than overall length.