Fuel Reserve Calculator
The Fuel You Plan Never to Use
Reserve fuel exists for exactly one purpose: to still be in the tanks after everything about the flight has gone according to plan, as a buffer against the things that don't — a holding pattern, a missed approach, an unexpected reroute. It's deliberately never touched under normal operations, which is precisely what makes it easy to underestimate. This calculator converts a burn rate and a required reserve time directly into the fuel quantity that needs to remain unspent at the end of the flight.
The Formula
The burn rate is divided by 60 to convert an hourly rate into a per-minute rate, which is then multiplied by however many minutes of reserve are required. The result is expressed in whichever fuel unit — gallons, pounds, or liters — matches the input.
Where This Calculation Matters
- Regulatory compliance — minimum reserve requirements are a hard rule, not a suggestion, and dispatching without them is a regulatory violation regardless of how favorable the weather looks.
- Diversion planning — reserve fuel is what's available if the destination airport becomes unusable and a diversion to an alternate is required.
- Realistic trip planning — total fuel load is trip fuel plus reserve, not trip fuel alone; leaving reserve out of the planning conversation is a common source of overly optimistic range estimates.
- Night and IFR operations — reserve requirements are typically higher for night and instrument flying, when diversion options and margin for error both matter more.
Commonly Cited Reserve Minimums
Regulatory reserve minimums vary by flight rules, time of day, and jurisdiction. The figures below reflect widely referenced U.S. planning minimums as a starting point — always confirm the exact requirement under the regulations governing your flight:
| Flight Rules | Typical Minimum Reserve |
|---|---|
| VFR, daytime | 30 minutes at normal cruise |
| VFR, night | 45 minutes at normal cruise |
| IFR | 45 minutes at normal cruise, after reaching the alternate (if one is required) |
How to Use This Calculator
- Enter the aircraft's fuel burn rate per hour, in the unit that matches your planning — gallons, pounds, or liters.
- Enter the required reserve time in minutes, based on the applicable flight rules and time of day.
- Select the fuel unit being used.
- Select Calculate to see the fuel quantity that must remain in the tanks at the end of the flight.
Related Calculations
Add this figure on top of the result from the Aircraft Fuel Burn Calculator to arrive at total required fuel load for a trip.