Reserve Fuel Calculator
Calculate FAA-required fuel reserves for airplane operations under FAR Part 91. Select your operation type to see the applicable regulation and compute your minimum planned fuel.
Why This Matters to Pilots
Fuel exhaustion is one of the leading causes of general aviation accidents. The FAA fuel reserve requirements in FAR 91.151 and 91.167 establish minimum standards, not targets. Experienced pilots routinely carry more than the regulatory minimum.
For IFR operations, the requirement to plan destination fuel, alternate fuel, and a 45-minute reserve separately ensures that each phase of the flight is independently accounted for. Combining them into a single number masks the individual requirements and can lead to inadequate planning.
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Frequently Asked Questions
This calculator is for educational and planning purposes only. Always refer to your aircraft's POH/AFM, current NOTAMs, and official weather briefings. No calculator is a substitute for pilot-in-command judgment or CFI guidance. Read our full Safety Disclaimer.
Regulatory content: 14 CFR 91.151, 14 CFR 91.167 • Last reviewed: 2026-07-30
Fuel Reserves in Depth
Reserve fuel is the quantity you plan to still have in the tanks when you land, and it exists to absorb the many small errors and surprises that separate a plan from a flight. Winds are rarely exactly as forecast, groundspeeds vary, a runway change lengthens your taxi, or a pattern gets extended for traffic. The reserve is the deliberate margin that keeps those ordinary variations from becoming an emergency, and the regulations set a legal minimum below which you may not plan.
The key mental shift is that reserve fuel is not trip fuel. It is untouchable by design: you compute your trip needs, then add the reserve on top, and you never plan to burn into it. This calculator makes that separation explicit so the fuel you load clearly distinguishes what the flight will use from what must remain.
Step-by-Step: How the Calculation Works
Under 14 CFR 91.151, day VFR flight requires enough fuel to reach the first intended landing point plus a reserve to fly at normal cruise for at least 30 minutes. For night VFR the reserve rises to 45 minutes. Instrument flight under 91.167 generally requires fuel to reach the destination, then the alternate if one is required, plus 45 minutes at normal cruise. The calculator converts the applicable minutes into gallons using your burn rate.
To size the reserve, multiply the required reserve time by your planned burn rate. Thirty minutes at 9 gallons per hour is 4.5 gallons; forty-five minutes is 6.75 gallons. Many pilots deliberately plan a full hour of reserve regardless of the legal minimum, because the regulatory figure is a floor, not a recommendation, and a larger personal reserve costs little in most light aircraft.
More Worked Examples
Example 1 — Night VFR reserve
You burn 10 gallons per hour and are planning a night cross-country. The 45-minute night VFR reserve is 0.75 hour × 10 = 7.5 gallons that must remain on landing. If your trip needs 28 gallons, you plan to load at least 35.5 gallons plus taxi fuel.
Example 2 — A conservative personal reserve
The legal day VFR minimum is 30 minutes, but you adopt a one-hour personal reserve. At 8 gallons per hour that is 8 gallons held back rather than 4. On a 40-gallon usable capacity that leaves 32 gallons for the trip, and you plan your legs and fuel stops around that stricter number.
Pilot Decision-Making Context
The reserve is where planning discipline is tested, because it is always tempting to shave it to avoid a fuel stop or carry more payload. The safer habit is to treat the reserve as fixed and adjust the rest of the plan around it: shorten a leg, add a stop, or reduce weight rather than dip into the margin. Accident history repeatedly shows that fuel emergencies stem from optimistic planning that treated the reserve as available.
Reserves also interact with weather. When conditions at the destination are marginal, a larger reserve gives you the fuel to hold, to attempt an approach a second time, or to divert to a better field. Sizing the reserve to the actual uncertainty of the flight — not merely to the legal minimum — is a hallmark of mature aeronautical decision-making.
More Questions Answered
Is the 30-minute VFR reserve enough?
It is the legal minimum for day VFR, not a target. Many pilots plan 45 minutes to an hour, because the regulatory figure leaves little room for the winds, delays, and diversions that routinely occur.
Does the reserve get calculated at cruise or approach burn?
The regulation specifies fuel to fly for the stated time at normal cruise power, so size the reserve using your normal cruise burn rate.
Can I count fuel I cannot actually use?
No. Reserve and trip planning must be based on usable fuel only. Unusable fuel in the tanks does not count toward any requirement.
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