Outboard fuel consumption calculator

How much fuel does an outboard use?

A useful rule for petrol outboards: a four-stroke burns roughly 0.09 US gallons — about 0.34 litres — per hour for each horsepower it is actually producing at full throttle. A carburetted two-stroke burns closer to 0.115 gallons per horsepower. The word "actually" matters: at an economical cruise a motor is producing about half its rated power, so it uses about half the fuel.

That means a 150 HP four-stroke uses around 13.5 gallons (51 litres) per hour flat out, but nearer 7 gallons (26 litres) at a sensible cruise. Sea state, hull load, trim and propeller choice all move the real figure, so use these numbers for budgeting and range planning rather than as a specification.

Planning your range safely

Work on the one-third rule: a third of your fuel out, a third back, a third in reserve. Head wind, chop and a heavy load can easily add 30% to consumption on the return leg, and fuel gauges on small boats are rarely accurate.

Cutting the bill

Most fuel is saved by finding the hull's efficient cruising speed — often only a few mph below where people habitually run — keeping the bottom clean, trimming the motor properly, and fitting a propeller that lets the engine reach its rated RPM instead of lugging. Modern fuel-injected four-strokes are typically 20–40% more economical than the two-strokes they replaced.