Boat fuel range calculator
How far you can go on the fuel aboard, and how far out you can safely turn around. Set your reserve, or use the one-third rule, and get your range, round-trip radius and runtime.
Usable tank capacity
Fuel per hour at cruise
At that burn rate
This is a planning estimate, not a promise. Real burn climbs with load, sea state, wind, current, a foul bottom, and the throttle, so published or best-case numbers run optimistic. Always keep a reserve, watch your actual gauge or fuel-flow, and never run a tank down offshore. Range is one-way on your usable fuel; the round-trip radius assumes you return on the same usable fuel and keep the reserve untouched.
How to plan boat fuel and range
Three numbers set your range: how much fuel you carry, how fast you burn it, and how fast you go. Divide your usable fuel by your burn rate to get runtime in hours, then multiply by your cruise speed for distance. The single most useful input is an honest burn rate, so measure your own gallons per hour at your normal cruise rather than trusting a brochure.
The part people skip is the reserve. Fuel exhaustion offshore is a genuine emergency, so decide up front how much you will hold back and do not plan to touch it. The classic approach is the one-third rule: a third to get there, a third to get back, a third in reserve. On a familiar day trip a lighter ten to fifteen percent may be enough. Either way, the round-trip radius above is the distance you can head out and still return on your usable fuel.
Frequently asked
How do I calculate my boat's fuel range?+
Range is your usable fuel divided by your burn rate, multiplied by your cruise speed. Usable fuel is your tank minus the reserve you want to keep. For example, 100 gallons with a one-third reserve leaves about 66 usable gallons; at 8 gallons per hour and 18 knots that is roughly 8 hours and about 148 nautical miles one way.
What is the one-third rule for boat fuel?+
A common safety practice: plan to use one third of your fuel to get there, one third to get back, and keep the final third as reserve. It builds in a margin for headwinds, adverse current, a longer route, or a slow return. This calculator's One third reserve preset applies it.
How many gallons per hour does my boat burn?+
It depends on the engine, boat and throttle, so the best number is your own: note the fuel used over a run at your normal cruise RPM, or read it from a fuel-flow gauge. As a rough starting point, many gasoline outboards burn near horsepower divided by 10 gallons per hour at cruise, and diesels less, but real burn varies widely, so measure yours.
How much fuel should I keep in reserve?+
There is no single right answer. Ten to fifteen percent is a light margin for a familiar day trip; the one-third rule is the conservative choice for longer or offshore runs. Whatever you pick, hold it back and do not plan to burn into it.
Is the calculated range safe to rely on?+
Treat it as a planning estimate, never a guarantee. Actual burn rises with load, sea state, wind, current, and a foul bottom, and manufacturer figures tend to be optimistic. Always carry a reserve, watch your real gauge or fuel flow, and never run a tank down offshore.
Fuel for the trip you’re actually planning
In Pathr, draw the route and it works out the distance, time and fuel for your boat, then tracks your range as you go. Free for your first two months on iOS.
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