Boat Fuel Consumption Calculator
Marine Engines Burn Fuel by the Hour, Not the Mile
A car's fuel economy is measured in miles per gallon because road speed and load stay fairly consistent. A boat is different — hull drag, current, and load change constantly, and outboard or inboard engines are rated by how many gallons or liters they burn per hour at a given throttle setting. That's why marine fuel planning starts with a burn rate rather than an economy figure, and why this calculator works either from a known burn rate and trip duration, or from distance and cruising speed when duration isn't known up front.
The Formula
By distance & speed: Trip Time = Distance ÷ Speed
Total Fuel = Burn Rate × Trip Time
Estimated Cost = Total Fuel × Fuel Price
Burn rate is entered in gallons or liters per hour, exactly as published in an engine's fuel consumption chart or observed from an onboard fuel-flow meter.
Where This Matters
- Range planning — before heading offshore, boaters need to know whether onboard fuel capacity covers the planned distance with a safety reserve.
- Trip budgeting — charter operators and weekend cruisers alike use burn rate and fuel price to estimate the true cost of a day on the water.
- Throttle setting comparisons — the same boat can burn dramatically more fuel per hour at wide-open throttle than at an efficient cruise setting, so comparing burn rates helps choose an economical cruising RPM.
- Refueling stops — on longer passages, knowing total fuel burned over a given duration determines where and how often to refuel.
Fuel Burned Over a Trip at 12 Gallons/Hour
| Trip Duration | Total Fuel | Estimated Cost |
|---|---|---|
| 1 hour | 12.0 gal | $51.00 |
| 2 hours | 24.0 gal | $102.00 |
| 4 hours | 48.0 gal | $204.00 |
| 6 hours | 72.0 gal | $306.00 |
| 8 hours | 96.0 gal | $408.00 |
Computed directly from Total Fuel = Burn Rate × Duration at a constant 12 gal/hr burn rate. Your engine's actual burn rate depends on load, hull design, and throttle setting.
How to Use This Calculator
- Choose calculation mode: By Trip Duration, or By Distance & Speed.
- Select Imperial (gallons) or Metric (liters) units.
- Enter the fuel burn rate per hour and, optionally, the fuel price per gallon or liter.
- Depending on the mode, enter either trip duration in hours, or distance and cruising speed.
- Select Calculate to see total fuel used and estimated cost.
Related Calculations
For road trips, the Fuel Cost Calculator handles the same duration-independent budgeting on land, and the Fuel Economy Calculator converts consumption between MPG and L/100km.