Fuel Burn Calculator

What is Fuel Burn?

Fuel burn is the rate at which an aircraft engine consumes fuel, typically expressed in gallons per hour (GPH) for piston aircraft or pounds per hour (PPH) for turbine engines. Knowing your fuel burn rate is essential for every phase of flight planning — it determines how much fuel you need to carry, how long you can stay airborne, and whether you have adequate reserves for your planned route.

Every cross-country flight plan begins with the same core question: do I have enough fuel to get there safely? To answer it, you need three things — your fuel burn rate, the expected flight time, and the required reserve. The fuel burn calculator at the top of this page handles the math for you, but understanding the underlying concepts is what makes you a safer, more capable pilot.

Fuel burn matters for several practical reasons:

• Legal fuel reserves — FAR 91.151 (VFR) requires enough fuel to fly to the first point of intended landing and then fly for 30 minutes (day) or 45 minutes (night). FAR 91.167 (IFR) requires 45 minutes beyond the farthest alternate or destination.
• Weight and balance — fuel is often the largest variable in your takeoff weight. Carrying more fuel than necessary reduces your useful load for passengers and baggage.
• Range and endurance planning — fuel burn determines whether you can make a nonstop leg or need a fuel stop, and how long you can hold or divert if weather deteriorates.
• Engine management — monitoring actual fuel burn in flight against your planned rate helps you detect problems early, such as a runaway mixture or a fuel leak.

How to Calculate Fuel Burn

The basic fuel burn calculation is straightforward:

Fuel Required = Fuel Flow Rate × Time

Where fuel flow rate is in gallons per hour (GPH) and time is in hours (or fractions of an hour). For example, if your fuel flow is 10 GPH and your flight time is 2.5 hours, you need 25 gallons of fuel.

To calculate endurance — how long you can fly on the fuel you have — reverse the formula:

Endurance = Usable Fuel ÷ Fuel Flow Rate

If you have 48 gallons of usable fuel and burn 8 GPH, your maximum endurance is 6 hours.

For a complete trip fuel calculation, you need to account for every phase:

Total Fuel = Taxi + Climb + Cruise + Descent + Reserve

• Taxi and run-up — typically 1–2 gallons for piston singles.
• Climb — fuel flow is higher during climb; use your POH climb fuel flow, not cruise.
• Cruise — the longest segment; use the GPH from your POH for the planned power setting and altitude.
• Descent — fuel flow drops during descent, but many pilots conservatively use the cruise rate.
• Reserve — the legal minimum (30 or 45 minutes at cruise fuel flow), though many pilots carry more.

Your POH or pilot's operating handbook is the authoritative source for fuel flow at various power settings, altitudes, and mixture configurations.

Step-by-Step Example

You are planning a VFR cross-country in a Cessna 172S. The flight leg is 180 nautical miles, your planned groundspeed is 115 knots, and you will fly during the day.

1. Determine flight time: 180 NM ÷ 115 knots = 1.57 hours (1 hour 34 minutes)
2. Look up cruise fuel flow: The POH shows 8.5 GPH at 65% power and 6,500 ft.
3. Cruise fuel: 8.5 × 1.57 = 13.3 gallons
4. Add climb fuel: The POH shows approximately 2.0 gallons to climb from pattern altitude to 6,500 ft.
5. Add taxi fuel: Allow 1.0 gallon for taxi, run-up, and initial departure.
6. Subtotal trip fuel: 1.0 + 2.0 + 13.3 = 16.3 gallons
7. Add VFR day reserve: 30 minutes at cruise burn = 8.5 × 0.5 = 4.25 gallons
8. Total fuel required: 16.3 + 4.25 = 20.55 gallons

The C172S has 53 gallons usable. After burning 20.55 gallons, you would have roughly 32 gallons remaining — well above the legal minimum. That extra fuel gives you flexibility for diversions, holding, or headwinds stronger than forecast.

Always round fuel calculations up, never down. If the math says 20.55 gallons, plan for at least 21.

Factors Affecting Fuel Burn

Fuel burn is not a fixed number. It changes with how you fly the aircraft and the conditions you fly in.

Power setting is the single biggest factor. At 75% power a typical piston engine burns significantly more fuel than at 55% power. Many pilots find a sweet spot around 60–65% power that offers a good trade-off between speed and economy.

Altitude affects fuel burn through mixture leaning. At higher altitudes, the air is thinner, and a properly leaned engine burns less fuel per hour. A Cessna 172 might burn 8.5 GPH at 4,000 ft but only 7.5 GPH at 8,500 ft at the same power setting, because the mixture is leaned more aggressively.

Mixture management is critical in normally aspirated engines. Running full rich above 3,000 ft density altitude wastes fuel and fouls spark plugs. Proper leaning per the POH can reduce fuel burn by 10–15% at cruise.

Wind does not change your fuel flow rate in GPH, but it changes how long you are airborne. A 20-knot headwind on a 200 NM leg adds roughly 15 minutes of flight time — that is an extra 2+ gallons at 8.5 GPH. Always use groundspeed, not TAS, when calculating flight time for fuel planning.

Temperature affects engine performance and density altitude. On a hot day, the engine produces less power at the same throttle setting, which can alter fuel flow. High density altitude also means a longer climb, which burns more fuel than the cruise phase.

Weight has a modest effect. A heavier aircraft requires more power to maintain altitude and airspeed, increasing fuel burn. This is more pronounced in turbine aircraft but still relevant in piston singles operating near max gross weight.

Aircraft condition matters too. Dirty air filters, fouled plugs, worn cylinders, or a slightly out-of-rig airframe all increase fuel burn. If your actual burn consistently exceeds the POH numbers, it may be time for maintenance.

Frequently Asked Questions

What is a fuel burn calculator?

A fuel burn calculator computes the amount of fuel required for a flight based on your fuel flow rate and expected flight time. It can also calculate endurance — how long you can fly on a given amount of fuel. Inputs are typically fuel flow in gallons per hour and time in hours or minutes, and the output is total fuel in gallons.

What is a typical fuel burn for a Cessna 172?

A Cessna 172S burns approximately 8.0–8.5 gallons per hour at 65% power in cruise, and up to 10–11 GPH during full-power climb. The exact figure depends on altitude, mixture setting, and aircraft condition. Always reference your specific aircraft's POH rather than relying on generic numbers.

How do I calculate fuel reserves?

Multiply your cruise fuel flow rate by the required reserve time. For VFR day flights, the legal minimum is 30 minutes of fuel at normal cruise consumption (FAR 91.151). For VFR night, it is 45 minutes. For IFR flights, you need 45 minutes at normal cruise after reaching your farthest alternate or destination (FAR 91.167). Many experienced pilots carry at least one hour of reserve regardless of the legal minimum.

Should I use fuel flow from climb or cruise for planning?

Use both. Climb fuel flow is significantly higher than cruise — often 20–30% more in piston aircraft. For an accurate fuel plan, calculate climb fuel and cruise fuel separately using the appropriate rates from your POH. A common shortcut is to use the POH's "time, fuel, and distance to climb" table for the climb segment and cruise GPH for the rest.

Does leaning the mixture really save that much fuel?

Yes. Proper mixture leaning at cruise altitude can reduce fuel burn by 10–15% compared to running full rich. At 8,000 ft, the difference might be 1.0–1.5 GPH in a typical four-cylinder engine. Beyond fuel savings, proper leaning prevents spark plug fouling and improves engine health. Always lean per your POH procedures — typically lean to peak EGT, then enrichen slightly if recommended.

How does wind affect my fuel calculation?

Wind does not change your fuel flow rate, but it changes your groundspeed and therefore your time en route. A headwind means you are airborne longer to cover the same distance, burning more total fuel. A tailwind reduces your time aloft and total fuel burned. Always calculate flight time using groundspeed, not true airspeed, to get an accurate fuel estimate. A strong headwind on a long leg can easily add 10–20% to your fuel requirement.