Fuel Per Navigation Leg Calculator
Calculate fuel needed for each leg of a voyage in nautical miles, km, or miles.
Returns leg time, reserve, burn per mile, and range against your tank.
How Fuel Per Navigation Leg Is Calculated
Marine and aviation navigation breaks a journey into legs, the segments between waypoints. Working out the burn on each leg separately is what tells you whether the fuel stop you planned is the right one.
The formula:
Time (hr) = Distance / Speed
Fuel = Time × Burn rate
Distance and speed just have to be in matching units. Enter 45 nautical miles at 7 knots, or 350 km at 200 km/h, and the hours come out the same way either time. This calculator converts for you, so you can enter the distance in nautical miles and the speed in km/h if that is what your instruments read.
Marine example (40 ft sailboat, auxiliary diesel):
- Burn: 4 L/hr at 7 knots motoring
- Leg: 45 nautical miles
- Time = 45 / 7 = 6.43 hours, which is 6h 26m
- Fuel = 6.43 × 4 = 25.7 L
- With the standard 20% reserve: 30.9 L
Aviation example (Cessna 172):
- Burn: 32 L/hr (8.5 US gal/hr)
- Cruise: 200 km/h (108 knots)
- Leg: 350 km (189 nm)
- Time = 350 / 200 = 1.75 hours
- Fuel = 1.75 × 32 = 56 L
- FAA day VFR reserve is 30 minutes of cruise, and most instructors want 45: 0.75 × 32 = 24 L
- Total = 80 L, against roughly 200 L usable in a 172S. Comfortable.
A note on how reserves are written. Aviation states reserves in time (30 or 45 minutes at cruise burn), because what kills you is running dry while holding, and holding burns by the clock rather than by the mile. Sailors state them as a percentage, because a passage plan already carries a distance and the wind decides how much of it you motor. This page uses percentages. To convert an aviation time reserve, divide it by your leg time: 45 minutes on a 1.75 hour leg is 43%.
Reserve rules worth knowing:
- Aviation day VFR: 30 minutes at cruise burn (45 recommended)
- Aviation night VFR and IFR: 45 minutes, reckoned from the alternate
- Coastal motoring: 20% is the usual working figure
- Offshore passage: the RYA line is a third in hand, and plenty of skippers carry double the calculated motoring fuel because a windless week is not a rare event
Fuel density, if you are doing a weight and balance: Avgas 100LL is 0.72 kg/L, Jet A-1 about 0.80, marine diesel 0.85. A full 200 L of diesel is 170 kg sitting wherever your tank is, which is enough to change a small boat’s trim.
How we build and check this calculator
This calculator runs entirely in your browser, so the numbers you enter stay on your device. The math behind it is written by hand and tested against worked examples and standard references before the page goes live.
SuperGlobalCalculator is independently built and maintained. See how we build and verify our calculators.