Fuel Burn Rate Calculator: Range, Endurance, and FAR Reserve for Pilots

What the FAA Requires for Aviation Fuel Reserves Under Part 91 in the US

Here is a situation every CFI has seen. A student asks: “How much fuel do I need?” The instinct is to answer, “Enough to get there plus 30 minutes.” That is technically accurate for VFR day flight, but it collapses three separate regulatory standards into one casual phrase, and it leaves out the other fuel items that add up fast: taxi and runup fuel, the climb to altitude, and the distinction between day and night rules that changes the reserve requirement by an entire 15 minutes.

14 CFR Part 91 has two separate fuel regulations. FAR 91.151 covers VFR flight. FAR 91.167 covers IFR flight. Neither one mentions a simple “30-minute rule” without context. Here is what they actually say:

Notice what these rules do not mention: taxi fuel, runup fuel, climb fuel, or any contingency allowance. All of those are implied by “enough fuel to reach the first point of intended landing” because you have to actually get airborne and climb to cruise before you can cover any distance. This calculator makes all those components explicit, calculates each one separately, and shows the VFR day, VFR night, and IFR totals in one view.

The Reserves Are a Floor, Not a Target

The 30-minute and 45-minute reserves are absolute minimums. Planning to land with exactly your legal reserve means any single disruption, any deviation from your plan, any ATC holding, any slight headwind increase, puts you below legal minimums in flight. Experienced pilots treat the legal minimums as the emergency threshold and adopt personal minimums of 45 minutes for day VFR, one hour for night VFR, and 1.5 hours for IFR. The extra fuel is cheap compared to the alternative.

How to Calculate Trip Fuel, Endurance, and Range for a GA Flight

The math behind a fuel calculation is four operations applied to five numbers. Most pilots who run into trouble are not bad at arithmetic. They skip the calculation entirely. This section walks through both the trip fuel formula and the endurance formula so you can understand what this calculator is doing under the hood.

Trip Fuel Formula

1. Flight time (hours) = Distance (nm) ÷ Groundspeed (kts)
2. Trip fuel = Fuel burn rate (GPH) × Flight time (hours)
3. Reserve (VFR day) = GPH × 0.5 (30 minutes = 0.5 hours)
4. Reserve (VFR night or IFR) = GPH × 0.75 (45 minutes = 0.75 hours)
5. Total VFR day = Taxi fuel + Climb fuel + Trip fuel + 30-min reserve
6. Total VFR night = Taxi fuel + Climb fuel + Trip fuel + 45-min reserve

Endurance and Range Formula

1. Available for cruise = Usable fuel – Taxi fuel – Climb fuel – Reserve
2. Endurance (hours) = Available for cruise ÷ GPH
3. Range (nm) = Endurance (hours) × Groundspeed (kts)

Endurance tells you how long you can fly on a given fuel load. Range tells you how far. Both are essential numbers for planning fuel stops on cross-country flights. Note that maximum endurance (longest time aloft) is achieved at a lower airspeed and power setting than maximum range (longest distance), because range depends on the ratio of distance covered per gallon of fuel burned.

The FAR 91.151 and 91.167 Reserve Rules Every US Pilot Must Know

Most GA pilots can recite the 30-minute rule. Fewer can tell you why the rule is 30 minutes and not some other number, or what the exception is, or exactly which flights require 45 minutes versus 30. This matters because the specific FAR you are operating under determines the legal minimum for your flight.

When 30 Minutes Applies

FAR 91.151(a)(1): The 30-minute reserve applies to day VFR operations in an airplane. Day is defined in 14 CFR 1.1 as the period between the beginning of morning civil twilight and the end of evening civil twilight. If your planned landing time is during civil twilight, you must use your aircraft’s navigation lights and you are operating under night rules for purposes of fuel. The practical implication: if you depart late afternoon and anticipate arriving after sunset, plan 45 minutes, not 30.

When 45 Minutes Applies

FAR 91.151(a)(2) for night VFR and FAR 91.167 for IFR both require 45 minutes. For night VFR, the 45 minutes is measured at normal cruising speed after reaching the destination. For IFR, the 45 minutes comes after completing the alternate leg if one is required. The alternate requirement itself depends on destination weather: if the airport’s weather for one hour before to one hour after estimated arrival does not meet the 1-2-3 rule (ceiling at least 2,000 feet, visibility at least 3 miles), an alternate is required on the IFR flight plan.

Personal Fuel Minimums: Beyond the FAR

Many flight schools, rental clubs, and commercial operators impose fuel minimums that exceed FAR requirements. A common policy is land with one hour of fuel for VFR day operations and 1.5 hours for any IFR. These policies exist because the FAA minimums leave no buffer for ATC delays, airspace closures, or a pilot who is simply slower to locate the airport than anticipated. Adopting personal minimums and sticking to them is a habit that aviation safety experts consistently identify as a key differentiator between experienced and inexperienced pilots.

Three Real Fuel Planning Scenarios from US Cross-Country GA Flights

Expert Tips for Fuel Planning and Fuel Economy at US Airports

Check Fuel Price Apps Before You Depart

Avgas prices vary significantly between airports, sometimes by $2.00 or more per gallon. On a 40-gallon fill, that difference is $80. Free apps and websites including FlyQ, ForeFlight, and AirNav let you compare 100LL prices at airports along your route. If your route takes you near a lower-cost airport and you have time for a 15-minute stop, the math often justifies it. This calculator’s cost feature helps you quantify the fuel cost at current prices, which makes the comparison concrete rather than approximate.

Use Actual Groundspeed Including the Wind

The single most common fuel planning error is using TAS instead of groundspeed. When you plan a 250 nm trip at 120 knots, you have to ask: 120 knots of what? If that is TAS and you are flying into a 25-knot headwind, groundspeed is 95 knots and your flight takes 2.6 hours, not 2.1 hours. The difference is 4.3 gallons of extra fuel on an 8.5 GPH burn rate. Check the forecast winds aloft for your cruise altitude on SkyVector, ForeFlight, or the Aviation Weather Center (aviationweather.gov) and use forecast groundspeed, not book TAS.

Add a Conservative Factor to Book Burn Rates

POH fuel burn figures represent ideal conditions: new engine, perfect mixture, clean airframe, standard atmosphere. Real-world GA aircraft burn 5 to 15 percent more than the book value. If your C172 POH says 8.2 GPH at 75 percent power and 8,000 feet, use 9.0 GPH for planning. The extra cushion costs you less than a gallon per hour and provides a real buffer against the difference between the idealized POH world and the actual air you fly through.

Log Actual Fuel Burns and Build Your Own Database

After every flight, record: planned burn rate, actual fuel used, flight time, and conditions. After ten flights in the same aircraft at similar power settings, you will have a personal burn rate that is more accurate than the POH for that specific airframe. Many pilots find their actual burn runs 8 to 12 percent above POH. Once you know your aircraft’s real number, your fuel calculations become significantly more reliable.

Quick Reference: Typical Fuel Burn Rates for Common US GA Aircraft

The values below are approximate cruise fuel burn rates at 75 percent power from representative POH data. Actual burn varies with altitude, temperature, mixture leaning, aircraft condition, and specific engine variant. Always use your aircraft’s POH for your planned power setting. Source: Representative POH data compiled from FAA Pilot’s Handbook of Aeronautical Knowledge (FAA.gov) and manufacturer publications.

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