Log in or create your free account

Enter your email and password to continue.

Terms of Service and Privacy Policy.

Forgot password?

BOAT PLANNING TOOL

Boat Fuel Calculator

How much fuel will your boat need?

Calculate the fuel required for your trip, safe reserve, cruising range, travel time and estimated cost using your boat's actual fuel burn.

Free. No account required.

Fuel Planning Inputs

All units are standard for recreational boating

Trip & Speed

NM

Need the route distance first? Plot your route in the free Trip Planner.

kn
kn
GPH
%
hrs

Performance & Consumption

GPH
GPH
Matches the Route Generator max-speed burn input. Pace and weather adjustments are derived from this value unless Efficient Speed uses the efficient inputs instead.
hrs
gal
Usable fuel can be less than nominal tank capacity.
$/gal

Estimated range is a planning value. Actual range can vary with sea conditions, current, wind, vessel load, engine condition, throttle use, and the amount of fuel that is practically usable.

Estimated Results

Total Distance

0.0 NM

Manual distance input

Total Travel Hours

-- h

Enter distance and inputs

Estimated Fuel

-- gal

Required + reserve

Adjusted Speed

-- kn

Weather adjusted

Expected Avg GPH

-- GPH

Across all running time

Estimated Range with Reserve

Enter fuel capacity

Optional usable-fuel estimate

Fuel Cost

--

Based on fuel price

Calculation Breakdown and JSON
Metric Value How computed

Turn this fuel estimate into a complete trip plan

Plan the route and stops, then recalculate mileage, travel time, fuel, reserve, and cost from the saved route. When departure approaches, turn the trip into a float plan. Free account required to save a trip.

Plan This Trip Free

Why Fuel Planning Matters

Safety First

Running out of fuel isn’t an option. Plan ahead and stay in control.

Weather Changes Everything

Wind, current, and sea state can significantly impact fuel burn.

Plan With Reserve

Build in reserve so you have options when conditions or plans change.

How Much Fuel Does a Boat Use Per Hour?

Boat fuel use is usually measured in gallons per hour, or GPH. There is no single GPH number that applies to every boat of a certain length or horsepower. Fuel burn changes with engine RPM and load, the hull, boat weight, propeller, trim, weather, current, sea state and other operating conditions.

The best number to use for trip planning is your boat's actual fuel burn at the speed you expect to cruise. If your engine display or fuel-flow system provides real-time GPH, use that value. Manufacturer performance tests for your specific boat and engine combination are the next-best reference.

Real Boat Fuel-Burn Examples

These manufacturer performance tests show how fuel burn and fuel economy vary among specific boat and engine combinations at specific test RPM settings.

Manufacturer boat fuel-burn test examples
Boat / Engine Test RPM Speed Fuel Burn Fuel Economy Source
G3 Boats 15 DLX / Yamaha F4040 hp single outboard 4,000 RPM 18.4 MPH 1.5 GPH 12.27 MPG Yamaha test data
Crestliner 1850 Fish Hawk / Mercury 150 Pro XS150 hp single outboard 3,000 RPM 21.3 MPH 3.6 GPH 6.0 MPG Mercury test data
Sportsman Open 232 / Yamaha F300300 hp single outboard 3,500 RPM 27.2 MPH 8.3 GPH 3.28 MPG Yamaha test data
Sea Hunt Gamefish 30 CB / Twin Yamaha F350Twin 350 hp outboards 3,500 RPM 35.9 MPH 17.2 GPH total 2.09 MPG Yamaha test data

These are examples, not lookup values for your boat. Manufacturer performance tests are conducted with specific hulls, loads, propellers and conditions. Your boat's actual fuel burn may be different.

GPH vs. MPG: What the Numbers Mean

GPH — Gallons Per Hour

GPH tells you how quickly the engines are consuming fuel. If your boat burns 8 GPH for three hours, the trip consumes about 24 gallons before reserve or other adjustments.

Fuel Used = Running Hours × GPH

MPG — Miles Per Gallon

MPG measures how far the boat travels for each gallon burned. A higher GPH does not automatically mean worse fuel economy if the boat is also traveling substantially faster.

MPG = Speed in MPH ÷ GPH

Nautical Miles Per Gallon

When working in knots and nautical miles, the same idea can be expressed as nautical miles per gallon.

NM per Gallon = Speed in Knots ÷ GPH

For trip planning, GPH tells you the burn rate while distance-per-gallon measurements help identify the more economical cruising point.

Why Boat Fuel Consumption Changes With Speed

Boat fuel consumption does not increase in a simple one-to-one relationship with speed. As speed and engine load change, the hull's resistance through the water, running attitude and propulsion efficiency also change.

On a planing boat, efficiency can change significantly as the boat transitions onto plane and then continues toward higher RPM. More throttle normally increases gallons per hour, but the most useful efficiency measurement is how much distance the boat travels for each gallon consumed.

This is why the lowest GPH is not automatically the best cruising speed. Idling may burn very little fuel per hour but cover very little distance. At the other extreme, high RPM can dramatically increase GPH without providing a proportional increase in speed.

How to Find Your Boat's Actual GPH

  1. Use onboard fuel-flow data

    If your engine display, multifunction display or fuel-management system reports real-time GPH, use that data while operating at your normal cruising speed.

    Yamaha states that its engine-management systems can continuously calculate fuel consumption and display information that lets operators evaluate fuel economy while underway.

  2. Find a manufacturer performance bulletin

    Search for a performance test matching your boat model, engine, horsepower and engine count. These reports commonly show RPM, speed, GPH and MPG at multiple throttle settings.

    Yamaha Performance Bulletins

  3. Compare with your own operating history

    Fuel added, engine hours and trip records can help establish a real-world baseline when the operating profile is reasonably consistent.

    One mixed-use tank does not automatically produce an accurate cruising GPH number.

  4. Use a conservative estimate when necessary

    If measured or manufacturer data is unavailable, use a conservative planning value and maintain additional reserve until you have enough real-world data to refine it.

Once you know your expected cruise GPH, enter it in the FloatPlanWizard calculator above along with distance, speed and reserve assumptions.

What Affects Boat Fuel Consumption?

Boat & Load

  • Passengers
  • Gear
  • Fuel and water carried
  • Optional equipment
  • Overall operating weight

More weight generally requires more power to achieve and maintain a given operating condition.

Hull & Running Surface

  • Hull design
  • Bottom condition
  • Fouling
  • Bottom paint
  • Added drag

Hull condition and drag affect how much power is required to move the boat through the water.

Engine, Propeller & Trim

  • Engine RPM and load
  • Propeller selection and condition
  • Engine trim
  • Trim tabs where applicable
  • Engine condition

Propeller setup and trim affect the boat's running attitude and how efficiently engine power is converted into forward motion.

Conditions & Route

  • Wind
  • Current
  • Waves and sea state
  • No-wake operation and idling
  • Route deviations
  • Temperature and elevation where applicable

The same boat can produce different fuel-burn results on different days or different sections of the same trip.

Further context: Yamaha performance data, Mercury fuel-efficiency guidance, and Mercury trim guidance.

Finding Your Most Efficient Cruising Speed

Your most economical cruising speed is the practical operating point where the boat covers the greatest useful distance for the fuel consumed. It is not necessarily the slowest speed, and it is rarely useful to assume one RPM or one percentage of wide-open throttle for every boat.

The best way to find it is to compare speed and fuel-flow data across several normal operating RPM settings. When using statute miles, divide MPH by GPH to calculate MPG. When using knots, divide knots by GPH to estimate nautical miles per gallon.

Manufacturer performance bulletins can provide a useful starting point, but real fuel-flow data from your own boat is better because it reflects your hull, load, propeller and operating conditions.

Don't optimize for GPH alone. Optimize for distance per gallon at a speed that makes sense for the trip.

Mercury cruising-speed guidance and Yamaha fuel-management guidance.

Boat Fuel Planning Example

Example: 60-Nautical-Mile Round Trip

  • 30 NM outbound
  • 30 NM return
  • 20-knot cruise
  • 8 GPH cruise fuel burn
  • $4.50 per gallon

Outbound

30 NM ÷ 20 kn = 1.5 hours 1.5 hours × 8 GPH = 12 gallons

Return

30 NM ÷ 20 kn = 1.5 hours 1.5 hours × 8 GPH = 12 gallons

Expected trip consumption

12 + 12 = 24 gallons

Estimated fuel cost

24 × $4.50 = $108

How Much Fuel Reserve Should You Carry?

The U.S. Coast Guard's A Boater's Guide to the Federal Requirements for Recreational Boats recommends practicing the One-Third Rule:

  • One-third of the fuel to go out
  • One-third to get back
  • One-third held in reserve

Treat the rule as a conservative fuel-management practice, not as a guarantee that a particular trip is safe. Wind, current, sea state, detours, no-wake zones and unexpected delays can increase actual consumption.

Use the Reserve Method control in the calculator above to apply the One-Third Rule or a percentage-based planning margin. Review the official U.S. Coast Guard boating guide for the One-Third Rule.

Boat Fuel Calculator FAQ

How much fuel does a boat use per hour?

Boat fuel use is measured in gallons per hour, but there is no single number that applies to all boats. GPH depends on the engine, RPM, hull, load, propeller, trim and operating conditions. For trip planning, use measured fuel-flow data or manufacturer performance data for your boat and engine whenever possible.

Can I estimate boat fuel burn from horsepower?

Horsepower alone is not enough to accurately predict cruise fuel burn. Generic horsepower formulas can produce rough theoretical estimates, especially near maximum engine output, but they do not account for hull efficiency, engine load, RPM, propeller, weight or conditions. Use actual GPH whenever possible.

Does slowing down always save fuel?

It normally lowers gallons burned per hour, but it does not automatically produce the best fuel economy per mile. The most economical cruise is the operating point that provides the best useful distance per gallon at an appropriate speed for the boat and trip.

How do I calculate how much boat fuel I need?

Divide trip distance by cruising speed to estimate running time, then multiply running time by your expected GPH. Add appropriate fuel for idling, changing conditions and reserve.

What is the best cruising speed for fuel economy?

It depends on the boat and engine combination. Compare GPH and speed at several normal operating RPM settings and look for the best distance-per-gallon result. Manufacturer performance bulletins and onboard fuel-flow data are the best places to start.

How much reserve fuel should I carry?

The U.S. Coast Guard recommends the One-Third Rule: one-third of the fuel for the outbound leg, one-third for the return and one-third held in reserve. Conditions and trip complexity may justify additional margin.

Should I use wide-open-throttle GPH in the calculator?

Only if you actually expect to operate at that fuel-burn rate. For normal trip planning, use the GPH associated with the speed and RPM you expect to cruise.

How accurate is the FloatPlanWizard fuel calculator?

The arithmetic is based on the values you enter. Its real-world accuracy therefore depends heavily on the accuracy of your speed, GPH, distance, idle-time and reserve assumptions. Weather, current, sea state, load and engine condition can change actual fuel use.

Sources & Further Reading