Boat Fuel Cost & Range Calculator

Divide the complete trip distance by average travel speed to get travel hours. Multiply hours by combined fuel consumption per hour, then multiply by fuel price. Use matching distance and speed units: nautical miles with knots, miles with mph, or kilometres with km/h.

For a return trip, enter both legs. Add any planned detours to that distance. A single average does not account for separate idling or trolling periods; calculate those separately and add their fuel to your plan.

An 80-nautical-mile round trip at 20 knots takes four hours. At 5 US gallons per hour it consumes 20 gallons. With fuel at $5 per gallon, that is $100 of fuel consumed.

If you want to retain one-third of departure fuel, the modeled departure requirement is 20 ÷ (1 − 1/3) = 30 gallons. Adding one-third to the 20-gallon trip burn gives only 26.67 gallons; that is a different buffer calculation. Try the example in the calculator to see both trip consumption and the reserve-inclusive requirement.

With 30 usable US gallons aboard, one-third retained, 5 GPH consumption and 20 knots, modeled total travel distance is 80 nautical miles. The out-and-back reach is 40 nautical miles from the start, assuming both legs have the same consumption and speed and there is no refueling.

The BOATsmart fuel guide describes the outward/return/reserve thirds convention. Treat it as a planning convention, not a guarantee that a particular route is safe. Conditions can change the fuel needed.

The figures above come from Yamaha’s Zodiac Open 5.5 / F115 bulletin. A test’s hull, loading and conditions matter. Look for a comparable manufacturer performance bulletin, then use your boat’s observed burn at the speed you plan to travel.

For twin engines, enter the total consumption of both engines. If your instrument already reports combined flow, do not multiply it again.

The optional model uses rated horsepower × engine count × a fuel coefficient × your assumed share of full-power burn. Gasoline uses 0.10 and diesel 0.055 US gallons per horsepower-hour; these are rough modeling coefficients, not a measured performance curve.

At the default 50% share, a single 150 HP gasoline engine produces a modeled 7.5 US GPH. Fifty percent here is not a throttle position. No universal cruise table is applied. Confirm actual consumption before relying on the fuel-carried or range result.

The tool uses US gallons, not Imperial gallons. One US gallon is 3.785411784 litres; one nautical mile is 1.852 kilometres. Changing units converts the entered quantities and per-unit fuel price rather than just changing their labels. Prices remain in USD.

Distance per fuel unit is speed ÷ hourly burn. At 20 knots and 5 US GPH, economy is 4 nautical miles per US gallon. Fuel aboard should be a usable amount, not simply the tank’s advertised capacity.