Miles Per Gallon Calculator

On the Water

Boat MPG Calculator

The Boat MPG Calculator estimates your vessel’s fuel efficiency on the water. Marine fuel economy works very differently from a car: water is far more resistant than a road, so even efficient boats burn a lot of fuel per mile. Knowing your real numbers helps you plan fuel stops, budget a day on the water, and avoid running low offshore.

Enter the miles travelled and the gallons used to get your boat’s MPG. Two optional inputs add useful detail: enter the hours you ran the engine to calculate gallons per hour (GPH) — often the most practical efficiency measure for boaters — and enter the gas price to see the total fuel cost of the outing.

GPH matters because boating is usually measured in time on the water rather than distance covered, and engine burn rate at cruise speed is a key planning figure. A small outboard might sip a few gallons per hour, while a large twin-engine powerboat can drink dozens. Speed has an outsized effect: pushing a hull onto a plane and then beyond its efficient cruise dramatically raises consumption. To stretch your fuel, find the sweet spot just above planing speed, keep the hull and propeller clean, trim properly, and lighten the load. Track these numbers across trips to spot changes early, and use our other calculators for road-vehicle fuel planning.

How to Use

  1. Enter the miles travelled on the water.
  2. Enter the gallons of fuel used.
  3. Optionally enter hours run to get gallons per hour.
  4. Optionally enter the gas price to get total cost.
  5. Click Calculate Boat MPG (or press Enter).

Related tools: MPG Calculator, RV MPG Calculator, Fuel Cost Calculator.

Got Questions?

Boat MPG Calculator FAQ

Divide the miles travelled by the gallons of fuel used. For example, 30 miles on 15 gallons = 2 MPG. Boat fuel economy is much lower than a car’s because of water resistance.

GPH measures fuel burned per hour of running time, calculated as gallons used ÷ hours run. It is often more useful than MPG for boats since cruising time matters more than distance.

It varies widely: small outboards may get 4–6 MPG, while large powerboats can be under 1 MPG. Trawlers and efficient hulls at low speed do best. Use GPH for a more practical comparison.

Water creates far more drag than a road. Planing hulls, heavy loads, rough water, and high speeds all sharply increase fuel burn, so boats use much more fuel per mile than cars.

Cruise at the most efficient speed (often just above planing), keep the hull clean, trim correctly, reduce excess weight, and maintain your engine and propeller.