Hull speed is the theoretical maximum efficient speed for a displacement hull, where the hull sits in a wave it cannot easily climb. The formula is 1.34 × √(waterline length in feet) in knots, or 2.43 × √(waterline length in meters) in knots. Planing hulls and multihulls can exceed this.

What is the difference between speed-over-ground and speed-through-water?

Speed-through-water (STW) is how fast the boat moves through the water itself. Speed-over-ground (SOG) accounts for current — a following current increases SOG above STW; a head-on current reduces it.

How many km/h is one knot?

1 knot = 1.852 km/h = 1.15078 mph = 0.514444 m/s. One knot is one nautical mile per hour, and one nautical mile equals 1.852 km.

How do I calculate boat fuel range?

Runtime (hours) = Fuel capacity ÷ Consumption rate. Range (nm) = Runtime × Speed. For example, 200 L tank, 20 L/hr consumption, 8 knots: runtime = 10 hr, range = 80 nm.

Can planing hulls exceed hull speed?

Yes. The hull speed formula applies only to displacement hulls. Planing hulls rise onto a plane at higher speeds and are not limited by the displacement hull speed formula. Multihulls also use different hydrodynamic principles.

Boat Speed Calculator

Name: Boat Speed Calculator
Availability: InStock
Author: Nham Vu

Calculate basic boat speed, theoretical hull speed, speed-over-ground vs speed-through-water, and fuel range in one tool.

Calculation Mode

Solve for Speed, Distance, or Time. Leave one field blank.

Distance

Time

Speed

Enter values and click Calculate

Speed Unit Reference

Unit	Knots	km/h	mph	m/s
1 knot	1.000	1.852	1.1508	0.5144
1 km/h	0.5400	1.000	0.6214	0.2778
1 mph	0.8690	1.6093	1.000	0.4470
1 m/s	1.9438	3.600	2.2369	1.000

1 nautical mile = 1.852 km = 1.15078 statute miles

Summary

Calculate basic boat speed, theoretical hull speed, speed-over-ground vs speed-through-water, and fuel range in one tool.

How it works

Choose a calculation mode: Basic Speed, Hull Speed, Current/SOG, or Fuel Range.
Enter the required values for your selected mode.
Results appear instantly in multiple units.
For hull speed, enter waterline length in feet or meters.
For current/SOG, choose "with current" or "against current" to adjust SOG and ETA.
For fuel range, enter fuel capacity, consumption rate, and boat speed to get nautical range.

Use cases

Estimating travel time between two ports using knots or mph.
Finding the theoretical maximum efficient speed of a displacement hull.
Accounting for tidal current when planning a passage.
Calculating how far a boat can travel on a tank of fuel.
Converting speed between knots, mph, km/h, and m/s.

Frequently Asked Questions

Last updated: 2026-06-10 · Reviewed by Nham Vu

Boat Speed Calculator

Calculation Mode

Basic Speed Result

Hull Speed Result

Speed Over Ground Result

Fuel Range Result