This calculator helps pilots plan their journeys with confidence, by estimating flight endurance from burn rate and fuel capacity, plus reserves you plan on top.

How the endurance calculator works

Endurance is the time an aircraft can keep flying on the fuel it has. The formula is simple: usable fuel divided by fuel burn per hour. Enter the usable fuel in gallons and the burn rate in gallons per hour, and the answer comes out in hours and minutes.

Use usable fuel, not total tank capacity. Some fuel in a tank can't be drawn by the engine, and your aircraft's flight manual lists the usable amount.

A worked example

Say you have 40 gallons of usable fuel and burn 9 gallons an hour. 40 divided by 9 is 4.44 hours, which is 4 hours and 27 minutes of endurance. That is the time to empty tanks, not the time you should plan to fly.

Subtract your reserve

The FAA sets a minimum fuel reserve. Under 14 CFR 91.151, a pilot flying an airplane under VFR must have enough fuel to fly to the first point of intended landing and then, at normal cruising speed, to fly at least 30 minutes by day or 45 minutes at night. Under 14 CFR 91.167, an IFR flight needs fuel to reach the first airport of intended landing, fly to the alternate airport, and then fly for 45 minutes at normal cruising speed, unless the alternate is not required.

With the example above, 4 hours 27 minutes of endurance leaves 3 hours 57 minutes of planned flying by day, or 3 hours 42 minutes at night, before the minimum reserve is touched. Many pilots plan a bigger margin than the regulations require.

Gallons and pounds

If your fuel quantity is in pounds, convert it before you enter it. The FAA's Pilot's Handbook of Aeronautical Knowledge uses 6 pounds per gallon for aviation gasoline, so 240 pounds of avgas is 40 gallons. Jet fuel is heavier, so use the figure from your flight manual.

What the estimate leaves out

  • Burn rate changes with power setting, altitude and mixture. Use the figure for how you'll fly the leg.
  • Climb, taxi and start-up burn more fuel than cruise.
  • Headwinds don't change endurance in time, but they cut the distance you can cover.
  • Measure the fuel in the tanks and check it against the gauges before flight.

For the wider picture on fuel systems, see types of aircraft fuel systems, and use the other calculators for weight and balance and pressure altitude.

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Disclaimer

The calculators on this site are provided for informational purposes only. Results are not guaranteed to be fully accurate or complete, and shouldn't be relied on for flight planning or any other purpose. It's the sole responsibility of the pilot to verify all flight planning information and to ensure the aircraft is safe and fit for flight. PilotPassion accepts no responsibility for errors or omissions in the information these calculators provide, or for any damage or injury resulting from their use. By using these calculators, you agree to use them entirely at your own risk.