Fuel endurance calculator
Endurance is how long you can stay airborne, which is a different question from how far you can go. Wind changes the distance but it does not change the time.
Calculator
This is an educational and planning aid. Use current official weather, your aircraft flight manual, and the rules that apply to your flight before you act on any figure here. See the aviation disclaimer.
What the result means
The headline figure is the time available before you reach the reserve you said you wanted to land with. That is the number to plan against.
Endurance to dry tanks is shown underneath for context. It is not a planning figure and should never be treated as one.
When this is useful
- Deciding whether a planned flight fits inside the fuel you have without refuelling.
- In flight, when the fuel state needs reassessing against a new destination or a hold.
- Working out the latest time you must be on the ground.
How it is calculated
Subtract the reserve from the usable fuel on board, then divide what is left by the fuel flow. The result is time. Every field uses the one fuel unit you select at the top of the page.
endurance = (usable fuel - reserve) / fuel flow
Worked example
- Usable fuel on board
- 120 litres
- Fuel flow
- 40 litres per hour
- Reserve to land with
- 30 litres
There are 90 litres available above the reserve, giving 2 hours 15 minutes of endurance. Dry tanks would be 3 hours.
Check: 120 litres minus a 30 litre reserve leaves 90 litres. At 40 litres per hour that is 2.25 hours, which is 2 hours and 15 minutes. The dry tank figure of 120 divided by 40 is exactly 3 hours, confirming the arithmetic.
Limitations
- Usable fuel is not tank capacity. Every aircraft has some unusable fuel that cannot feed the engine, and the flight manual states how much.
- Fuel flow varies with power setting and is highest in the climb, so a cruise figure flatters a short flight.
- Fuel gauges in light aircraft are not precise instruments. Dipping the tanks and knowing what you uplifted is more reliable.
Common mistakes
- Entering total tank capacity instead of usable fuel.
- Entering a zero reserve, which turns this into an endurance to dry tanks calculation.
- Confusing endurance with range. Into a strong headwind you can run out of fuel long before you expected to, because the distance shrank while the time did not.
Sources
- Pilot's Handbook of Aeronautical Knowledge, aircraft performance , US Federal Aviation Administration