Vessel Fuel Consumption Calculator
Fuel planning is essential for safe marine passages. This calculator uses your vessel's fuel burn rate in gallons per hour (GPH), your cruising speed in knots, and your fuel tank capacity in gallons to calculate range under the one-third safety rule, total fuel for a specific passage, and estimated fuel cost. GPH burn rate is available from engine specifications or measured empirically. Always add a safety margin for adverse weather, current, and reserve, and never plan to arrive with empty tanks.
Fuel consumption formulas
NMPG = Speed (kts) / Burn (GPH)
Total range = Capacity * NMPG
Safe range (1/3 rule) = (Capacity / 3) * NMPG
Fuel for passage = Distance / NMPG
Passage cost = Fuel for passage * Price per gallon
The 1/3 safety rule reserves two-thirds of capacity: one third outbound, one third return, one third reserve.
Fuel planning best practices
- Measure your actual burn rate at cruising RPM over a known distance to calibrate your planning.
- Add 10-15% to fuel estimates for headwinds, foul current, or rough seas.
- Identify intermediate fuel stops on long passages as a contingency.
- NMPG decreases significantly in rough seas as the engine works harder against wave resistance.
Vessel fuel consumption: frequently asked questions
How do I find my vessel's fuel burn rate?
Fuel burn rate (GPH) is typically found in the engine manufacturer's specifications, your vessel's owner manual, or through empirical measurement by noting fuel consumed over a known distance and time. Burn rate varies significantly with throttle setting and sea conditions.
What is the 1/3 fuel rule?
The standard safety rule is to reserve fuel in thirds: one third for the outbound leg, one third for the return trip, and one third in reserve for unexpected delays, headwinds, or detours. This rule is especially important for offshore passages.
How does speed affect fuel consumption?
For displacement hulls, fuel consumption roughly follows the cube of speed. Doubling speed increases fuel consumption approximately eightfold. Planing hulls have a speed range where they become more efficient once on plane. Operating just below planing speed is the least efficient regime.
What is nautical miles per gallon (NMPG)?
NMPG is the marine equivalent of miles per gallon: the distance you can travel on one gallon of fuel at a given speed. NMPG = Speed (knots) / Burn rate (GPH). It is useful for comparing fuel efficiency at different throttle settings.
How should I account for wind and current in fuel planning?
Head winds and adverse currents increase resistance and fuel consumption. Add at least 10-15% to your fuel estimate for adverse conditions. Always carry more fuel than the calculation suggests and identify intermediate fuel stops on long passages.
Official sources
- US Coast Guard Boating Safety: USCG Boating Safety Division.
- National Geospatial-Intelligence Agency: Bowditch American Practical Navigator.
Reviewed by the CalculatorHub team, edited by James Graham, 15 June 2026. See our methodology.