Fuel Range Calculator
Plan your range using the 1/3 rule and check if you can make it to your destination.
Vessel & Fuel Data
Total Range
Hours of Fuel
10.0 hrs
50 gal ÷ 5 gal/hr
Total Range
120 nm
10.0 hrs × 12 kts
The 1/3 Rule
Divide your fuel into three equal thirds.
16.7 gal — how far you can go
40 nm
16.7 gal — return trip
40 nm
Emergency / never dip into this
16.7 gal
Destination Range Check
Remaining fuel after round trip to 30 nm
GO — enough fuel for round trip
One-way fuel: 12.5 gal
Round-trip fuel: 25.0 gal
Tank capacity: 50 gal
Fuel remaining after round trip: 25.0 gal (50%)
Exam Tip — The 1/3 Rule
The USCG 1/3 fuel rule: use 1/3 to go out, keep 1/3 to return, and hold 1/3 in reserve. Never depart if you cannot make it back on 2/3 of your tank. This rule applies regardless of vessel size and is frequently tested on all license exams. Remember: the reserve third is for emergencies — current, weather delays, or detours — not part of your planning range.