Fuel Reserve Endurance
Calculator
Results
- Usable endurance (hours)
- 4.021739
- Usable endurance (minutes)
- 241.304347
- Total endurance to dry tanks (hours)
- 4.565217
Aviation and marine results
| Usable endurance (hours) | 4.021739 |
| Usable endurance (minutes) | 241.304347 |
| Total endurance to dry tanks (hours) | 4.565217 |
formula-map diagram
- Usable endurance (hours)
- 4.021739
- Usable endurance (minutes)
- 241.304347
- Total endurance to dry tanks (hours)
- 4.565217
Aviation and marine relationship
Formula
Usable endurance = (fuel on board − reserve) ÷ fuel flow= 4.0217391304348
Note
This is a simplified model: it applies a standard navigation, performance or seamanship formula to the numbers you entered. True airspeed and density altitude use the ISA troposphere model for dry air and ignore humidity, compressibility and instrument or position error, so they are not a substitute for your aircraft's flight manual or an air data computer. Wind, climb, descent and fuel figures assume a steady wind and a constant speed and fuel flow for the whole leg; they ignore manoeuvring, holding, taxi and start-up fuel, terrain, turbulence and air traffic control routing. Takeoff distance scales an entered sea level figure by a rule-of-thumb percentage per 1000 ft of density altitude and is not a certified performance chart. Weight and balance results depend entirely on the arms and weights you enter and must be checked against the approved loading envelope. Hull speed is the classic 1.34 × √LWL displacement estimate, boat fuel burn is a horsepower-based approximation, anchor scope is a rule of thumb, and the rule of twelfths is a linear approximation of a sinusoidal tide that does not hold in all locations. Always use official charts, tide tables, the aircraft or vessel manuals and current weather, and treat these numbers as planning estimates only.
More in Aviation and marine
See all →Frequently asked questions
What is fuel reserve endurance and why is it required?+
It's the amount of flight time your remaining fuel would allow after subtracting mandatory reserves, typically expressed in minutes or hours. Reserves exist to give a safety margin for unexpected headwinds, holding, a missed approach, or diversion to an alternate airport.
How is reserve endurance calculated?+
Usable fuel is divided by the aircraft's fuel burn rate to get total endurance, then the required reserve time (for example 30 or 45 minutes depending on rules and day/night VFR or IFR operation) is subtracted to leave the reserve endurance, or the fuel remaining above minimum reserves.
What's a common misconception about fuel reserves?+
Pilots sometimes treat reserve fuel as a cushion to dip into if a flight runs long, but regulatory reserves are meant to be untouched under the planned flight — landing with less than minimum reserve fuel is treated as a safety event in most jurisdictions, not just a preference.
Why does fuel burn rate used in this calculation matter so much?+
Small errors in the assumed burn rate compound over a long flight. Using an optimistic cruise burn figure instead of a rate that accounts for climb, leaning, and reserve power settings can make the calculated endurance look better than what you'll actually have in the tanks.
Does unusable fuel factor into this calculation?+
It should. Every aircraft has a small amount of unusable fuel that cannot be drawn into the engine due to tank and fuel system geometry, and only usable fuel should be entered into an endurance calculation — using total fuel capacity instead will overstate your actual reserve endurance.