Boat Fuel Consumption Calculator

Work out boat fuel consumption instantly with clear inputs, formula shown and shareable results.

About Boat Fuel Consumption Calculator

A petrol outboard uses roughly 0.21 litres per hour per horsepower at full throttle, and load falls steeply as throttle is reduced. Cruising at 70% throttle uses only about 40% of wide-open-throttle fuel, which is why the most economical cruise is well below maximum.

Formula

Boat fuel

L/h = hp x (throttle fraction)^2.5 x 0.21 for petrol; diesel is roughly 0.17

Worked example

With the default values below, Boat Fuel Consumption Calculator returns Fuel used of 64.57. Change any input above and every figure here is recalculated in your browser.

Inputs used

Engine power: 150 hp
Cruise throttle: 70 %
Hours running: 5 h
Fuel price: 1.75

Results

Fuel used: 64.57 L
Consumption rate: 12.91 L/h
Fuel cost: $113.00
Cost per hour: $22.60

Step by step

1Values used
2Boat fuel
3Fuel used= 64.57 L
4Consumption rate= 12.91 L/h
5Fuel cost= 113.00
6Cost per hour= 22.60

Assumptions and limits

The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 2 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

Why is the exponent above two?

Because propeller load rises roughly with the cube of speed while throttle position maps non-linearly onto that. An empirical exponent near 2.5 fits observed consumption well.

What is the one-third rule?

Plan one third of fuel for the outward passage, one third to return, and one third in reserve. It is standard practice for offshore boating.