Boat Fuel Consumption Calculator

About this calculator

Calculate boat fuel burn, trip fuel costs and modeled range with independent marine units and a user-selected reserve.

How to use the Boat Fuel Consumption Calculator

Choose Fuel Consumption, Plan a Trip or Boat Range. Each mode has its own inputs and independent unit choices, kept only in this tab. Valid edits calculate immediately. Use Announce result for an accessible spoken summary. Reset all modes restores every documented example and unit, returns to Fuel Consumption, clears copy feedback and focuses Fuel used.

Measure fuel consumption and cost

Enter fuel used, distance traveled, trip time in decimal hours and fuel price. The result shows average gallons or liters per hour, distance per unit of fuel, trip fuel cost, cost per distance and average speed. Use matching measurements from the same trip. For example, 1.5 hours means 1 hour 30 minutes.

Plan a trip’s fuel

Enter the full distance you intend to model, constant cruising speed, fuel burn, price and your selected reserve. Include a return leg in the entered distance if needed; this calculator does not add it automatically. An optional tank capacity adds a planned-allocation comparison. Fuel cost is for the modeled trip consumption, excluding unused reserve.

Model boat range

Enter fuel onboard, constant hourly burn, cruising speed and your selected reserve. The result reports fuel available to the model after reserve, endurance and modeled distance. It is not a navigation route, a fuel-sufficiency decision or a voyage safety assessment.

Marine units and currency

Open Units and currency to choose fuel volume in US gal or L, distance in nmi, mi or km, speed in knots, mph or km/h, burn in US gal/hour or L/hour, and price per US gal or per L. The range mode omits currency and price. Liters, nautical miles and knots can be used together. Economy follows the selected distance and fuel-volume units, such as nmi/US gal or nmi/L.

Changing a unit converts affected accepted inputs rather than reinterpreting their numbers. For example, 25 US gal becomes 94.6352946 L; 60 nmi becomes 111.12 km; 24 knots becomes 44.448 km/h. A price of 4.20 per US gal becomes approximately 1.10952 per L in the same currency. Invalid affected inputs must be corrected before a unit change. Conversions retain numerical precision; display results round separately.

The defined factors are 1 US liquid gallon = 3.785411784 L, 1 international nautical mile = 1.852 km, and 1 statute mile = 1.609344 km. One knot is one nautical mile per hour. Imperial gallons are not supported. Currency choices are USD, EUR, GBP, CAD and AUD; changing currency keeps the numeric price and changes its denomination, with no exchange-rate conversion.

Formulas and reserve methodology

The engine normalizes fuel to liters, distance to kilometers, time to hours, speed to km/h, burn to L/hour and price to currency/L. It validates all denominators before calculation. Internal arithmetic retains precision; fuel, economy, speed and distance results normally display two decimals and costs use currency precision. Tiny positive quantities show a less-than display instead of a misleading zero. Hours/minutes are rounded for readability.

Fuel consumption

Fuel burn (L/hour) = fuel used ÷ trip hours. Economy (km/L) = distance ÷ fuel used. Trip fuel cost = fuel used × price per liter. Cost/km = trip cost ÷ distance. Average speed (km/h) = distance ÷ trip hours. These are entered-trip averages; the calculator does not estimate burn from horsepower or engine type.

Trip planning

Trip hours = distance ÷ speed. Trip fuel = trip hours × hourly burn. Trip cost = trip fuel × price. If r is selected reserve percent ÷ 100, planned fuel = trip fuel ÷ (1 − r). Reserve amount = planned fuel − trip fuel.

Reserve definition: The percentage of planned onboard fuel intended to remain unused by the modeled trip. The user selects it; 25% is an editable example, not a recommendation. For 45 US gal of trip consumption and 25%, planned fuel is 45 ÷ 0.75 = 60 US gal, leaving 15 US gal in the model. Multiplying 45 by 1.25 gives 56.25 and does not implement this definition.

Range

Usable modeled fuel = fuel onboard × (1 − r). Reserve fuel = fuel onboard − usable modeled fuel. Endurance hours = usable modeled fuel ÷ hourly burn. Modeled range = endurance × speed. At 80 US gal onboard and 25%, this makes 60 US gal available to the model and 20 US gal reserved. The same reserve definition applies in trip and range modes.

Tank-capacity comparison

Capacity utilization = planned fuel ÷ entered tank capacity. Capacity margin = entered capacity − planned fuel. The bar uses entered capacity as its denominator, not original fuel, measured onboard fuel or vessel range. It appears only when capacity is supplied. At more than 100%, the bar is visually capped while the full utilization and amount above capacity remain visible in text. Planned fuel is never reduced to fit the tank.

For example, 60 US gal planned against 80 US gal capacity uses 75% and leaves a 20 US gal allocation margin. Against 50 US gal, the same plan uses 120% and exceeds capacity by 10 US gal. Neither comparison determines whether a trip can be completed. Entered tank capacity may differ from actually usable fuel.

Worked examples and reset defaults

The following outputs are generated by the same engine as the interactive calculator. Consumption defaults are 25 US gal, 60 nmi, 3 hours and 4.20 USD/US gal. Trip defaults are 120 nmi, 24 knots, 9 US gal/hour, 4.20 USD/US gal, 25% example reserve and no tank capacity. Range defaults are 80 US gal, 10 US gal/hour, 25 knots and 25% example reserve. All modes start with US gal, nmi, knots and US gal/hour; price modes start in USD per US gal.

Boat Fuel Consumption example

Fuel burn

8.33 US gal/hour

Fuel economy

2.40 nmi/US gal

Trip fuel cost

$105.00 USD

Cost per distance

$1.75 USD/nmi

Average speed

20.00 knots

Boat Trip Fuel Plan example

Estimated trip fuel

45.00 US gal

Distance

120.00 nmi

Estimated trip time

5.00 hr (5 hr 0 min, rounded)

Estimated fuel cost

$189.00 USD

Selected reserve

25.00% (15.00 US gal)

Planned fuel amount

60.00 US gal

Boat Range Estimate example

Modeled range

150.00 nmi

Fuel onboard

80.00 US gal

Selected reserve

20.00 US gal / 25.00%

Usable modeled fuel

60.00 US gal

Fuel burn

10.00 US gal/hour

Cruising speed

25.00 knots

Modeled endurance

6.00 hr (6 hr 0 min, rounded)

Assumptions, bounds and limitations

This is arithmetic based on entered quantities and constant speed, fuel burn and price. Actual consumption and range can change with conditions and vessel operation—for example, wind, current, sea state, speed/throttle changes, maneuvering or idling, vessel loading, engine/propeller condition and routing detours. These examples are not a complete list of marine hazards. The model does not adjust for weather, tides, routes, engine condition or changes during a trip.

There is no navigation system, voyage safety approval, engine diagnostic, manufacturer burn database, legal/compliance assessment or emergency fuel recommendation. The selected reserve is not assessed for adequacy. No source endorses BuzCalculator or certifies a modeled range.

Implementation limits in canonical units: fuel used/onboard and optional tank capacity 0.001–1,000,000 L; distance 0.001–1,000,000 km; time 0.001–10,000 hours; speed 0.001–300 km/h; burn 0.001–100,000 L/hour; price 0–10,000 currency units/L; selected reserve 0–95%. Converted equivalents apply in other units. These bounds limit arithmetic, not vessel suitability or recommended operation. Reserve 100% is rejected to avoid division by zero. Tiny conversion noise at an exact bound is normalized to that bound.

Zero price is valid and produces zero costs without changing consumption or range arithmetic. Required blanks, grouped numbers, exponents, hex, nonfinite numbers and values outside the bounds are rejected. Blank tank capacity means no comparison. Implausible combinations can still produce large finite estimates; input acceptance is not an operating recommendation.

Copy results and privacy

Copy results copies the accepted current mode’s formatted estimate and limitations only after you press the button. If clipboard access fails, a labeled selectable textarea appears for manual copying. Invalid results cannot be copied. Inputs, modes and unit choices stay in tab memory; there is no saved boat profile, account, persistent storage, financial-state URL, Share action or network calculation. Reset or reload restores examples.

Boat Fuel Consumption Calculator FAQ

How do I calculate gallons per hour?

Divide fuel used in US gallons by trip time in hours. Using 25 US gal over 3 hours gives about 8.33 US gal/hour. Use values from the same trip; the result is an average rather than an engine-specific burn curve.

Can I use liters with nautical miles and knots?

Yes. Choose each unit independently in the units disclosure. Changing fuel volume does not force distance or speed to change. Burn and price basis also have their own choices.

What is the difference between a knot and a nautical mile?

A nautical mile is distance, equal to exactly 1.852 km. A knot is speed: one nautical mile per hour. A statute mile uses a different factor, 1.609344 km.

Why is 25% reserve not calculated by adding 25% to trip fuel?

The reserve here is a share of total planned onboard fuel intended to remain unused. For 45 US gal of consumption, dividing by 0.75 gives 60 US gal planned, of which 15 US gal is 25%. Adding 25% to 45 uses a different denominator.

Is the example reserve a safety recommendation?

No. The field is user-selected, and the 25% example and 95% implementation maximum are not recommendations. The Coast Guard’s thirds guidance is attributed separately; this calculator does not determine an adequate reserve for a voyage.

What does the tank bar measure?

It compares planned fuel against the entered tank capacity. It does not measure actual fuel onboard or establish usable tank volume. If the plan exceeds capacity, the numerical excess remains visible even though the bar stops at 100%.

Does the planned trip include a return journey?

Only if you include that distance in your input. No return leg or route is added automatically. Use the total distance you intend to model, with the same constant speed and burn assumptions across it.

Does fuel cost include buying the reserve?

No. The displayed trip fuel cost is estimated trip consumption multiplied by the entered price. Planned onboard fuel includes the selected unused reserve, so it is a different quantity. The tool does not know what fuel you already own.

Does this tell me whether a trip is safe or I have enough fuel?

No. This is a constant-speed, constant-burn arithmetic model. Real conditions, vessel operation, routing and usable versus nominal tank fuel can change the outcome. It does not determine fuel sufficiency or replace voyage planning and operator judgment. Modeled range is not navigation guidance, a guarantee or confirmation of voyage safety.

Does changing currency convert the fuel price?

No. Currency changes only relabel the numeric price; enter the appropriate price yourself. Changing per-gallon versus per-liter basis does convert the physical price within the same currency. Zero price is allowed.

Sources and method review

Reviewed September 26, 2026. NOAA supports the international nautical-mile and knot definitions. The U.S. Coast Guard’s recreational boating guide describes allocating thirds to outward travel, return travel and reserve. That guidance is separate from this calculator’s user-selected reserve field; it does not establish a universal percentage or endorse this model. The example 25% is a project example only.

• NOAA: Nautical miles and knots (opens in a new tab)
• U.S. Coast Guard: A Boater’s Guide to the Federal Requirements for Recreational Boats, Fuel Management (opens in a new tab)
• NIST: Unit conversion factors (opens in a new tab)

Formulas are dimensional arithmetic. Reserve semantics, example values, input bounds and constant-input assumptions are explicit project choices. References are static and are not fetched during calculation. This is a project method/content review, not professional marine certification.