Fuel Consumption Calculator ⛽
Calculate boat fuel consumption rate (GPH/L/h) and total fuel needed for your trip. Enter engine horsepower, throttle %, and cruise duration.
How to Use the Fuel Consumption Calculator
Enter engine type (inboard/outboard), horsepower, throttle percentage, cruise duration, and fuel type to calculate fuel consumption. Gasoline coefficient is 0.10, diesel is 0.055.
Actual fuel consumption may vary based on sea conditions, hull condition, and load. Use the calculation results as a reference only.
For long-distance voyages, prepare an additional 20-30% fuel reserve beyond the calculated amount.
Boat & Marine Calculator - Introduction
Estimate how much gasoline or diesel your boat burns per hour from three numbers you already know: rated horsepower, throttle setting, and trip length. The estimator uses brake-specific fuel consumption (BSFC) — about 0.5 lb of fuel per hp-hour for gasoline 4-strokes and 0.3 lb for diesels — and converts the result to gallons per hour and liters per hour so you can size your fuel order and plan reserves.
How It Works
GPH ≈ horsepower × (throttle% ÷ 100) × fuel coefficient × engine factor. The gasoline coefficient is 0.10 and diesel is 0.06; the engine factor adjusts for 2-stroke outboards (×1.35), 4-stroke outboards (×1.0), and inboards (×0.95). A 200 hp gasoline outboard at 75% throttle therefore burns 200 × 0.75 × 0.10 × 1.0 = 15 GPH (about 57 L/h). Multiply by hours underway to get total fuel for the trip.
Usage Scenarios
- Day trip with the right reserve: A 150 hp 4-stroke at 70% cruise burns roughly 10.5 GPH. For a 4-hour run that is 42 gallons; add the conventional one-third reserve and plan to depart with at least 56 gallons aboard.
- Switching from a 2-stroke to a 4-stroke: Replacing a 150 hp 2-stroke (×1.35 engine factor) with a modern 4-stroke (×1.0) at the same throttle drops hourly burn from about 15.2 GPH to 11.3 GPH — roughly 26% less fuel for the same trip.
- Diesel vs gasoline range comparison: A 300 hp diesel at 60% throttle burns about 10.3 GPH; an equivalent 300 hp gasoline engine burns about 18 GPH. The same 200-gallon tank yields ~19 hours under diesel power versus ~11 hours on gasoline.
Frequently Asked Questions
How do I calculate boat fuel consumption?
Fuel consumption (GPH) = HP × throttle% × fuel coefficient. Gasoline coefficient is 0.10, diesel is 0.055. For example, a 200HP gasoline engine at 75% throttle: 200 × 0.75 × 0.10 = 15 GPH. Multiply by trip duration for total fuel needed.
How much fuel does a 150HP outboard use per hour?
At 75% throttle: 150 × 0.75 × 0.10 = 11.25 GPH (gasoline). At full throttle: 150 × 1.0 × 0.10 = 15 GPH. Actual consumption varies with hull efficiency, sea conditions, and load.
What is the difference between inboard and outboard fuel consumption?
Inboard engines are generally more fuel-efficient at cruising speeds due to better hull integration. Outboard motors are more efficient at lower speeds. Both use the same coefficient formula, but actual efficiency depends on hull design and operating conditions.
How much extra fuel should I carry for safety?
Always carry 20-30% more fuel than calculated. The 'rule of thirds' is popular: use 1/3 going out, 1/3 coming back, keep 1/3 in reserve. For offshore trips, carry even more reserve fuel and file a float plan.
Can I contact you for help planning my boating trip?
Yes! For personalized advice on marine trip planning and calculations, reach out to us at card.workshop@gmail.com. We're happy to help.