Vessel Fuel Range Calculator
How far a boat can go on a tank depends on three things: how much usable fuel it carries, how efficiently it travels (speed divided by burn rate), and how much you hold back in reserve. This calculator combines them. It subtracts your chosen reserve from the tank capacity, computes fuel economy in nautical miles per unit of fuel, and returns the cruising range and the endurance in hours at your planned speed. Burn rate rises steeply with speed for most powerboats, so a modest reduction in cruise speed can stretch range considerably. Keep a generous reserve, since real consumption varies with load, sea state, and current.
Vessel fuel range formula
Usable fuel = fuel capacity * (1 - reserve% / 100)
Fuel economy = cruise speed / fuel burn
Cruising range = usable fuel * fuel economy
Endurance = usable fuel / fuel burn
Speed in knots over burn in gallons per hour gives nautical miles per gallon, so multiplying by usable gallons yields nautical miles of range. Keep all fuel figures in the same unit.
Fuel planning notes
- The rule of thirds keeps about a third of fuel in reserve: a third out, a third back, a third spare.
- Burn rate climbs steeply with speed on planing boats, so slowing down extends range.
- Use a measured burn rate at your planned cruise speed, not an optimistic figure.
- Increase the reserve for open water, adverse current, or uncertain consumption.
- Gallons or litres both work as long as you do not mix them in one calculation.
Vessel fuel range: frequently asked questions
How do I calculate a boat's fuel range?
Multiply the usable fuel by the boat's fuel economy, which is cruise speed divided by fuel burn rate. Usable fuel is the tank capacity less your safety reserve. The result is the range in nautical miles. Endurance, the hours you can run, is the usable fuel divided by the burn rate.
What reserve should I keep?
A widely used cruising guideline is the rule of thirds: one third of fuel out, one third back, and one third held in reserve, which is about a 33 percent reserve. Conditions, range to the next fuel, and the reliability of your consumption figures should all push the reserve higher rather than lower.
Why does speed change the range so much?
Fuel burn rises steeply with speed for planing and semi-displacement boats, often much faster than the speed itself, so pushing harder usually cuts range. Backing off to an efficient cruise speed can dramatically extend how far a given tank will take you. Always use the burn rate that matches the speed you plan to run.
How accurate is this estimate?
It is only as good as the burn rate you enter. Real consumption varies with load, sea state, hull fouling, current, and trim. Measure your actual burn at your planned cruise speed in similar conditions, and keep a generous reserve, because range estimates that look fine on paper can fall short at sea.
Can I use gallons or litres?
Yes, as long as you stay consistent. If fuel capacity is in gallons and burn rate is in gallons per hour, the units cancel and range comes out in nautical miles when speed is in knots. The same holds for litres and litres per hour. Do not mix gallons with litres in the same calculation.
Official sources
- U.S. Coast Guard Navigation Center: navigation and voyage planning references.
- BoatUS Foundation: boating safety and fuel planning resources.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.