What this calculator shows
Fuel endurance is the time a quantity of usable fuel would last at a steady fuel burn rate. This calculator reports estimated total endurance, the fuel quantity represented by the entered reserve, and the time remaining after subtracting that reserve.
It uses the fuel quantity and fuel flow that you enter. It does not decide how much fuel should be carried or whether a reserve is sufficient for a particular flight.
How to use the calculator
Enter usable fuel in US gallons, the planned fuel burn in gallons per hour, and a reserve duration in minutes. The result updates as you type, and the input values are mirrored in the page URL.
Use a burn rate appropriate to the planned power setting and conditions from the aircraft's POH or AFM. This calculation assumes that rate remains constant for the entire period.
How the calculation works
Endurance divides usable fuel by the hourly fuel burn. Reserve fuel converts reserve minutes to hours before multiplying by the burn rate:
endurance hours = usable fuel / fuel burn rate
reserve fuel = reserve minutes / 60 x fuel burn rate
time after reserve = endurance hours - reserve minutes / 60
Example calculation
With 30 gal usable fuel, a burn rate of 8 gal/hr, and a 45 min reserve:
- Total endurance:
30 / 8 = 3.75 hr, or3 hr 45 min. - Reserve fuel:
45 / 60 x 8 = 6 gal. - Time after reserve:
3.75 - 0.75 = 3 hr.
If the entered reserve is longer than the estimated endurance, the time after reserve is negative. This indicates that the values do not cover the entered reserve.
Assumptions and limitations
The calculation assumes the entire entered quantity is usable and that fuel flow stays constant. It does not add taxi, run-up, climb, or contingency fuel, account for unusable fuel, or model changes in mixture, power, altitude, or wind.
Fuel quantity and burn rate are aircraft and operation specific. Verify usable fuel and expected fuel flow against the aircraft documentation and current conditions. The computed endurance is for training and reference only.
Sources and methodology
The calculation is fuel quantity divided by a constant hourly rate, with reserve time converted to the same units. Use the applicable aircraft POH or AFM for usable fuel, fuel flow, and required planning margins. Applicable regulations and procedures must be checked separately.
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