Boat Fuel Calculator
Enter your trip distance, cruising speed, fuel burn and reserve to estimate how long you will be underway and how much fuel to carry.
How to plan boat fuel
- Enter the trip distance in nautical miles and your cruising speed in knots.
- Enter your fuel burn at that speed in gallons per hour.
- Set a safety reserve and read the hours underway and total fuel needed.
Examples
100 nm cruise at 20 knots
distanceNm = 100, speedKnots = 20, gallonsPerHour = 8, reservePercent = 10
5 hours underway, 40 gal for the trip, 44 gal with reserve
Frequently asked questions
How do I find my gallons per hour?
Check the engine maker's fuel curve for your cruising rpm, or measure it: note fuel used and engine hours over a known run. Higher speeds usually burn far more per hour.
How much fuel reserve should I keep?
A common boating rule is the third tank rule: a third out, a third back and a third in reserve, which is about a 50 percent reserve. Many cruisers plan at least 10 to 20 percent.
Why use nautical miles and knots?
One knot is one nautical mile per hour, so distance in nautical miles divided by speed in knots gives hours directly, with no conversion factor.
Does this account for current, wind or sea state?
No. It assumes a steady speed and burn rate. Head seas, current and a foul bottom all raise consumption, so add margin in rough conditions.
Can I plan a round trip?
Yes. Enter the total round-trip distance, or run the numbers one way and double the base fuel, then add your reserve on top.
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