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.

What is the Aviation Fuel Reserve Calculator (VFR/IFR)?

Calculate total minimum fuel for a flight from trip distance, groundspeed, and burn rate, applying the FAR 91.151 VFR 45-minute reserve or the FAR 91.167 IFR alternate-plus-reserve rule, and compare it against your planned fuel on board. It runs free in your browser on Gera Tools, with nothing uploaded.

Aviation Fuel Reserve Calculator (VFR/IFR)

Name: Aviation Fuel Reserve Calculator (VFR/IFR)
Creator: Gera Tools
License: https://creativecommons.org/licenses/by/4.0/

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Running out of fuel is one of the most preventable causes of general aviation accidents, and the FARs set clear minimum reserves for good reason. 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 — showing a surplus or a shortfall at a glance.

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 for the distance to the alternate. The reserve is the required minutes converted to hours, multiplied by burn rate. A taxi, run-up, and climb allowance covers the fuel consumed before cruise.

trip fuel      = (distance / groundspeed) × burn
alternate fuel = (alt distance / groundspeed) × burn   (IFR only)
reserve fuel   = (reserve minutes / 60) × burn
minimum        = taxi_climb + trip + alternate + reserve
surplus        = fuel_on_board − minimum

VFR vs IFR reserve rules

FAR 91.151 (VFR): enough fuel to fly to the first point of intended landing, plus a reserve to fly at normal cruise speed for at least 45 minutes (day or night). The tool adds that 45-minute block on top of trip fuel.

FAR 91.167 (IFR): enough 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 alternate distance you enter.

When alternate fuel is required under IFR

Under FAR 91.169, an alternate airport is required unless the destination weather forecast is at or above certain ceilings and visibility for the hour before and after arrival — the so-called “1-2-3 rule.” When an alternate is required, it must be filed in the flight plan and its fuel is included in the IFR minimum.

Worked example

A Cessna 172 (burns 8 gallons/hour) flying 150 nm at 110 knots groundspeed, VFR:

Trip time: 150 / 110 = 1.36 hours
Trip fuel: 1.36 × 8 = 10.9 gal
Reserve (45 min): 0.75 × 8 = 6.0 gal
Taxi/climb allowance: 2.0 gal
Minimum required: 18.9 gal

With 30 gallons on board, the surplus is 11.1 gallons — comfortable, but the legal reserve should never be your planning target. Most experienced pilots aim for a personal reserve well beyond the regulatory minimum.

Planning beyond the legal minimum

The legal reserve is not a target — it is the floor. Real planning should add margin for:

Headwind error: winds-aloft forecasts can be off; a heavier-than-expected headwind burns extra fuel.
Holding delays: busy terminals may issue holds of 10–20 minutes.
Reroutes: ATC may vector you around weather, adding distance.
Alternate distance: if you are uncertain whether you’ll need an alternate, plan for one anyway.

Keep every fuel input in the same units (all gallons or all litres). Burn and groundspeed figures should come from the actual aircraft POH and the day’s winds-aloft forecast, not from memory.