Fuel Burn per Nautical Mile Calculator
Knowing how much fuel a boat burns per nautical mile turns an hourly fuel flow into a measure of passage efficiency and range. Because one knot is one nautical mile per hour, dividing the hourly fuel flow by speed over ground gives fuel per nautical mile directly. Enter your fuel flow per hour, your speed over ground, and a passage distance to get fuel per nautical mile, nautical miles per gallon, and the total fuel needed.
Fuel burn per nautical mile formula
Fuel per nm = fuel flow per hour / speed over ground (knots)
Nautical miles per unit = speed over ground / fuel flow per hour
Total fuel = fuel per nm * passage distance
The unit of the result matches your fuel flow unit (gallons or litres). Add a reserve to the total fuel for safety.
Worked example
- Fuel flow 4 gallons per hour at 8 knots over ground.
- Fuel per nm = 4 / 8 = 0.50 gallons per nautical mile.
- Nautical miles per gallon = 8 / 4 = 2.00.
- Over 120 nm: 0.50 * 120 = 60.00 gallons, plus reserve.
Fuel burn per nautical mile: frequently asked questions
How do I find fuel burn per nautical mile?
Divide the fuel flow per hour by the speed over ground in knots: fuel per nautical mile = fuel flow (per hour) / speed (knots). Because a knot is one nautical mile per hour, the hours cancel and you get fuel per nautical mile directly. Slower, more efficient cruising lowers this figure.
How do I get nautical miles per gallon?
Nautical miles per gallon is the reciprocal of fuel burn per nautical mile, or equivalently speed over ground divided by fuel flow per hour. At 8 knots burning 4 gallons per hour, that is 8 / 4 = 2.00 nautical miles per gallon.
Why use speed over ground rather than speed through the water?
Fuel efficiency over a passage depends on how far you actually travel relative to the seabed, which is speed over ground. Current can raise or lower it. Using speed through the water would understate the effect of a favourable current and overstate progress against a foul one.
How do I estimate total fuel for a trip?
Multiply fuel burn per nautical mile by the passage distance in nautical miles. The calculator does this when you enter a distance, and you should add a reserve on top for safety, weather, and diversions.
Official sources
- U.S. Coast Guard: recreational boating, fuel planning.
- NIST: unit conversions (gallon, litre, nautical mile).
Reviewed by the CalculatorHub team, edited by James Graham, 19 June 2026. See our methodology.