What does FAR 91.151 require for VFR?

For VFR flight in an airplane, FAR 91.151 requires enough fuel to fly to the first point of intended landing plus a reserve to fly at normal cruise for at least 45 minutes, day or night. The tool adds that 45-minute reserve on top of trip fuel.

How does the IFR rule differ?

FAR 91.167 requires fuel to the destination, then to the most distant alternate when one is required, plus 45 minutes at normal cruise. The IFR mode adds alternate fuel based on the distance you enter, which the VFR mode omits.

Are these reserves a target or a minimum?

They are legal minimums, not targets. Many operators add a personal reserve of an hour or more for weather, holding, headwind error, and unexpected reroutes. Landing with only the legal reserve in the tanks leaves no margin for the unexpected.

What units does it use?

It is unit-agnostic. Enter burn, taxi allowance, and fuel on board all in the same units, either US gallons or litres, and the results come back in those same units. Just keep every fuel figure consistent.

Why include a taxi and climb allowance?

Fuel is burned before the en-route cruise begins, during start, taxi, run-up, takeoff, and the climb, often at higher than cruise burn. Adding a fixed allowance keeps the plan honest, since the trip-fuel calculation alone assumes cruise burn for the whole leg.

Aviation Fuel Reserve Calculator (VFR/IFR)

Running out of fuel is one of the most preventable causes of accidents, and the regulations set clear minimum reserves. This calculator works out trip, alternate, and reserve fuel under the VFR rule (FAR 91.151) or the IFR rule (FAR 91.167) and compares the total against the fuel you plan to carry.

How it works

Trip fuel is flight time multiplied by burn rate, where flight time is distance divided by groundspeed. In IFR mode, alternate fuel is added the same way using the distance to the alternate. The reserve is the reserve minutes converted to hours, multiplied by burn rate. A fixed taxi, run-up, and climb allowance covers the fuel used before cruise.

trip fuel      = (distance / groundspeed) x burn
alternate fuel = (alt distance / groundspeed) x burn   (IFR)
reserve fuel   = (reserve min / 60) x burn
minimum        = taxi + trip + alternate + reserve

The tool then subtracts the minimum from your planned fuel to show a surplus or a shortfall.

Notes

These outputs are legal minimums. Real planning should add margin for headwind error, holding, weather, and reroutes, and the burn and groundspeed figures should come from the actual aircraft POH and the day’s winds. Keep every fuel input in the same units, gallons or litres.