Fuel Flow Rate Calculator
Solve the classic fuel-flow relation ṁf = TSFC · T for any of its three unknowns — fuel flow rate, thrust-specific fuel consumption, or thrust — with step-by-step math, a clean engine schematic, and companion fuel-burn metrics.
TSFC is the engine's "efficiency number"
TSFC measures how many kilograms of fuel are burned per newton of thrust per hour. A lower TSFC means the engine converts fuel into thrust more efficiently. Modern high-bypass turbofans reach TSFC ≈ 0.03–0.04 kg/(N·h) in cruise, while older turbojets run 0.08–0.10 and turboprops (converted from BSFC) come in around 0.10–0.16 in equivalent terms. The steady march of TSFC downward is the main reason jet fuel burn per seat has fallen by over 50% since the 1960s.
Fuel flow scales linearly with thrust
For a given engine, doubling thrust doubles fuel flow. This is why cruise fuel burn is so closely tied to how much thrust the aircraft needs. Reducing drag — by flying slower, flying higher, or improving the airframe — reduces thrust, which reduces fuel flow, which extends range. The relationship is the fundamental link between aircraft drag and aircraft fuel burn.
Thrust is not constant during flight
Thrust varies continuously with throttle setting, altitude, Mach number, and engine bleed. In cruise the aircraft is trimmed so thrust equals drag, so the fuel flow relation becomes ṁf = TSFC · D. In climb, extra thrust is needed to raise the aircraft against gravity, so fuel flow rises. In descent, thrust is reduced and fuel flow falls sharply — a jet at idle descent burns only 10–15% of its cruise fuel flow.
Altitude improves specific range
Because a turbofan's TSFC falls with altitude (colder air improves the thermodynamic cycle) while drag falls with density, flying higher reduces fuel burn per kilometre even though the aircraft flies faster. This is why airliners climb as they burn off fuel and why the optimum cruise altitude rises during a long flight. The fuel flow relation captures this directly: at the same thrust, thinner air and lower TSFC combine to give lower fuel flow.
How to Use This Calculator
The fuel flow relation links three quantities: ṁf, TSFC, and T. Pick which one you want the tool to solve, then fill in the other two.
1. Choose what to solve for
Pick ṁf, TSFC, or T from the toggle. The calculator rearranges ṁf = TSFC · T automatically for whichever you choose.
2. Use realistic presets
Presets cover typical values: fuel flow from 20 to 12,000 kg/h, TSFC from 0.030 to 0.150 kg/(N·h), and thrust from 2,500 to 300,000 N — spanning light piston aircraft to large turbofans.
3. Match units carefully
TSFC is in kg/(N·h) and thrust in N, giving fuel flow in kg/h. If you have TSFC in lb/(lbf·h) or thrust in lbf, convert first — or use the unit converter further down the page. The hint under each field shows the value in alternative units.
4. Read the result and verdict
The result card shows the fuel flow in kg/h plus the equivalent kg/s, lb/h and L/h (assuming Jet-A density). A colour-coded verdict classifies the flow rate from light piston through commuter, regional jet, narrow-body, and wide-body classes.
5. Check the schematic and charts
The schematic shows fuel flowing from the tank into the engine, and thrust emerging out the back. The chart plots fuel flow against thrust for three TSFC values.
6. Switch to Advanced for depth
Advanced mode adds a chart of ṁf vs. TSFC, a sensitivity check on a +1% input change, and companion metrics including specific range, fuel per unit distance, and fuel burn in lb/h, L/h, and gal/h.
What This Tool Offers
Built around the classic fuel-flow relation ṁf = TSFC · T, the fundamental link between engine efficiency, thrust, and fuel burn.
Three-way solving
Solve for fuel flow rate, thrust-specific fuel consumption, or thrust. The calculator rearranges the formula for whichever variable you choose.
Clean engine schematic
A fuel-tank-to-engine-to-thrust diagram with the fuel flow arrow on the inlet side and the thrust arrow on the exhaust side, both scaled in thickness with magnitude.
Flow-class verdict
Each result is classified from very low (light piston) through commuter, regional jet, narrow-body, wide-body, up to very large transport, with a coloured badge.
Multi-unit hints
Each field shows the value converted to related units — kg/s, lb/h, and L/h for fuel flow; lb/(lbf·h) for TSFC; lbf and tonne-force for thrust.
Dual comparison charts
ṁf vs. thrust for three TSFC values, plus an advanced ṁf vs. TSFC chart for three thrust values.
Reference tables
Typical TSFC by engine type, fuel flow by aircraft class, and a full variable reference table with unit conversion notes.
Reference Tables & Conversions
A fuel flow unit converter, a TSFC lookup grid, and typical values by engine type.
Fuel flow rate unit converter
Fuel Flow Lookup at TSFC = 0.050 kg/(N·h)
Computed from ṁf = TSFC · T with TSFC = 0.050 kg/(N·h). Values in kg/h.
| Thrust (N) | TSFC 0.030 | TSFC 0.040 | TSFC 0.050 | TSFC 0.070 | TSFC 0.100 |
|---|
Typical TSFC and Fuel Flow by Engine Type
Representative cruise values. TSFC depends strongly on flight condition; values shown are for typical cruise.
| Engine / aircraft class | Typical thrust (N) | TSFC kg/(N·h) | Fuel flow (kg/h) | Notes |
|---|---|---|---|---|
| Light piston (Cessna 172) | 1,500 (equiv.) | 0.150 | ≈ 225 (equiv.) | BSFC ≈ 0.25 kg/(kW·h); actual flow ≈ 30–40 kg/h |
| Light turboprop (Caravan PT6) | 4,000 (equiv.) | 0.100 | ≈ 400 (equiv.) | Actual flow ≈ 150–200 kg/h at cruise |
| Regional turboprop (Q400) | 14,000 (equiv.) | 0.090 | ≈ 1,260 (equiv.) | Two PW150 turboprops |
| Regional jet (E175) | 30,000 | 0.055 | ≈ 1,650 | Two CF34-class turbofans |
| Narrow-body jet (B737) | 50,000 | 0.050 | ≈ 2,500 | Two CFM56-class turbofans |
| Wide-body jet (B777) | 150,000 | 0.045 | ≈ 6,750 | Two GE90-class turbofans |
| Very large (A380) | 220,000 | 0.043 | ≈ 9,460 | Four Trent 900-class turbofans |
| Supersonic (Concorde) | 170,000 | 0.100 | ≈ 17,000 | Four Olympus turbojets at M 2.0 |
Variable Reference
| Symbol | Meaning | Typical range | Units |
|---|---|---|---|
| ṁf | Fuel mass flow rate | 10 – 20,000 | kg/h |
| TSFC | Thrust-specific fuel consumption | 0.03 – 0.16 | kg/(N·h) |
| T | Thrust | 10² – 5×10⁵ | N |
| BSFC | Brake-specific fuel consumption (for shafts) | 0.20 – 0.35 | kg/(kW·h) |
| ρJet-A | Density of Jet-A fuel | 0.804 – 0.812 | kg/L |
| ρAvgas | Density of Avgas 100LL | 0.68 – 0.72 | kg/L |
What Does ṁ_f = TSFC · T Measure?
The fuel flow relation connects three quantities that any propulsion engineer works with every day: the rate at which fuel mass is consumed (ṁf), the efficiency with which the engine converts that fuel into thrust (TSFC), and the amount of thrust being produced (T). Together they describe how much fuel the aircraft burns at any operating condition, and hence how far it can fly, how long it can stay aloft, and how much it costs to operate.
Fuel Flow Formula
The defining relationship is:
Rearranged to solve for the other two unknowns:
T = ṁf / TSFC
When the aircraft is in steady level flight, thrust equals drag, so the relation can also be written:
which links fuel burn directly to aircraft drag rather than to thrust — the starting point for range and endurance calculations.
Fuel Flow Variables
| Symbol | Meaning | Notes |
|---|---|---|
| ṁf | Fuel mass flow rate | Mass per unit time; kg/h here, kg/s in SI base units |
| TSFC | Thrust-specific fuel consumption | Fuel mass per unit thrust per unit time; lower is better |
| T | Thrust | Net propulsive force; equals drag in steady level flight |
| D | Drag | Equals thrust in level unaccelerated flight |
| BSFC | Brake-specific fuel consumption | Used for shaft engines: fuel per unit shaft power per unit time |
How Each Variable Affects Fuel Burn
Because the relation is linear in both TSFC and T, each has a proportional effect on fuel flow. Halving TSFC halves fuel burn at the same thrust; halving thrust halves fuel burn at the same TSFC. In practice both change together: at higher altitude the engine produces less thrust but also has a lower TSFC, and at lower speed the aircraft needs less thrust but the engine is operating away from its best TSFC point. The engineer's job is to find the combination of altitude, speed, and engine setting that minimises the product TSFC · T for the mission being flown.
That product is exactly what determines the specific range — the distance flown per unit of fuel burned. For a jet aircraft, specific range is maximised when the product of TSFC and drag is minimised, which happens at the speed and altitude where the aircraft's lift-to-drag ratio is highest and the engine's TSFC is lowest. In practice this is the long-range cruise condition published in the aircraft flight manual, and it is where airlines fly on long sectors. On shorter sectors, higher speeds are used because the time saving is worth more than the small extra fuel burn.
Fuel Flow Calculation Examples
ṁf = 0.050 × 50,240 = 2,512 kg/h
TSFC = 2,512 / 50,240 = 0.050 kg/(N·h)
T = 2,512 / 0.050 = 50,240 N
Specific range = V / ṁf = 230 / 2,512 = 0.0916 m/kg = 91.6 m/kg ≈ 0.0916 km/kg
Frequently Asked Questions
TSFC is the mass of fuel burned per unit of thrust produced per unit time, expressed here in kg/(N·h). It is the engine's efficiency number in the sense that a lower TSFC means the engine extracts more thrust from each kilogram of fuel. Modern high-bypass turbofans reach TSFC values around 0.03–0.04 in cruise, while older turbojets are in the 0.08–0.10 range. This is why every commercial aircraft in service today uses a high-bypass turbofan rather than a turbojet: at the same thrust, the turbofan burns roughly half the fuel.
For propeller aircraft the engine is rated in shaft power, so the natural efficiency measure is brake-specific fuel consumption BSFC in kg/(kW·h). To convert to equivalent TSFC, you need the propeller efficiency and the flight speed: TSFC = BSFC / (ηp · Vkm/h) × 3600 ... in practice the conversion is easier to do numerically. For a turboprop with BSFC ≈ 0.30 kg/(kW·h), ηp ≈ 0.85 and V ≈ 500 km/h, the equivalent TSFC is roughly 0.09–0.10 kg/(N·h). This is why turboprops show higher equivalent TSFC than turbofans but still burn less fuel on short sectors — they are more efficient in terms of shaft power, and their lower cruise speeds reduce drag.
In steady level flight the aircraft is in equilibrium, so thrust exactly equals drag. Drag varies with airspeed, altitude, aircraft weight, and configuration (flap, gear, spoilers). As the aircraft burns fuel it gets lighter, so drag falls and thrust is reduced — that is why the autothrottle continually reduces fuel flow over a long cruise. Wind and temperature also affect the required thrust. In a turn the aircraft must produce extra lift, which increases induced drag, which requires more thrust. Throughout the flight the pilot or autothrottle is continuously adjusting thrust to maintain the desired flight condition, and fuel flow follows.
Two competing effects occur as altitude increases. First, the lower air density reduces drag at the same true airspeed, so less thrust is required and fuel flow falls. Second, lower ambient temperature improves the thermodynamic efficiency of the engine, so TSFC falls as well. Both effects point the same way, which is why fuel burn per kilometre is lowest at high altitude. The optimum cruise altitude for a given aircraft and weight is where the decrease in TSFC and drag is balanced against the reduction in available thrust from the thinner air — the aircraft's ceiling. This optimum is why long-haul airliners fly at 35,000–40,000 feet.
Specific range is the distance flown per unit mass of fuel burned, usually expressed in km/kg or nautical miles per pound. It is related to fuel flow by SR = V / ṁf, where V is true airspeed. Since ṁf = TSFC · T = TSFC · D in level cruise, specific range can also be written SR = V / (TSFC · D) = (L/D) / (TSFC · W) × V ... in words, specific range is highest when the aircraft has a high lift-to-drag ratio and the engine has a low TSFC. Both conditions are met at high altitude and at the speed for best L/D, which is why long-range cruise is flown there.
Multiply kg/h by 2.20462 to get lb/h, or divide lb/h by 2.20462 to get kg/h. Because the fuel density of Jet-A is about 0.806 kg per litre, you can also convert to volume: L/h = kg/h / 0.806, and US gal/h = L/h / 3.785. Avgas 100LL has a slightly lower density of about 0.70 kg per litre, so volumetric conversions for piston aircraft use a different factor. The unit converter card above performs all these conversions in one step.
Yes, significantly. TSFC is lowest near the engine's design point and rises at both very low and very high thrust settings. At idle the engine is running far from its design point and TSFC can be 2–3 times its cruise value. At maximum thrust the engine is running hotter and TSFC rises modestly. This is why descent fuel flow is not simply zero even when thrust is near zero — the engine still burns fuel to keep running, and its TSFC at that low setting is very poor. The single-value TSFC used in this calculator is only accurate near the operating point for which it is quoted.
Variables
| Symbol | Quantity | Unit |
|---|---|---|
| mdot_f | Fuel flow rate | kg/s |
| TSFC | Thrust-specific fuel consumption | kg/(N*s) |
| T | Thrust | N |
What it means
Fuel flow rate is the rate at which fuel is consumed by the engine. It is directly proportional to thrust and TSFC. This parameter is used to calculate fuel consumption for a given flight phase and to estimate total fuel required for a mission. It also appears in the Breguet range equation. Understanding fuel flow is essential for fuel planning, cost analysis, and environmental impact assessment.
Worked example
Fuel Flow Rate – Two Examples
Real‑World| Parameter | Value |
|---|---|
| TSFC | 1.8×10⁻⁵ |
| T | 20,000 N |
| Parameter | Value |
|---|---|
| TSFC | 2.0×10⁻⁵ |
| T | 25,000 |
Common mistakes
- Fuel flow rate: ṁ_f = TSFC · T.
- TSFC: Thrust specific fuel consumption (kg/(N·s) or 1/s).
- T: Thrust (N).
- Units: kg/s.
- TSFC varies with throttle setting, altitude, and Mach.
Applications
Fuel flow rate, ṁ_f = TSFC·T, relates the engine fuel consumption to thrust. It is used to compute fuel burn for missions, to size fuel systems, and to select engines. Engineers use this to estimate flight costs and to plan refuelling stops. By understanding fuel flow rate, aerospace engineers can design efficient propulsion systems and operate aircraft economically. The TSFC (thrust specific fuel consumption) is a key performance parameter for gas turbine engines.
- Engine fuel consumption prediction for flight planning
- Fuel system sizing (pumps, lines, tanks)
- Cost analysis for airline operations
- Environmental impact assessment (CO₂ emissions)
- Engine performance monitoring and diagnostics
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