Calculator Inputs
Use BSFC for power-producing machines and TSFC for thrust-producing systems. The responsive input grid shows three columns on large screens, two on smaller screens, and one on mobile.
Example Data Table
These example rows show realistic operating points. Use them to test the calculator, compare units, and verify your own results.
| Mode | Fuel Flow | Output | Speed | Approx. SFC |
|---|---|---|---|---|
| BSFC | 18 kg/h | 75 kW | 0 m/s | 240 g/kWh |
| BSFC | 42 lb/h | 120 hp | 0 m/s | 350 lb/hp·hr × 0.001 ≈ 0.350 |
| TSFC | 0.34 kg/s | 25,000 N | 220 m/s | 13.6 mg/N·s |
| TSFC | 3200 kg/h | 90 kN | 780 km/h | 9.88 mg/N·s |
Formula Used
Brake Specific Fuel Consumption
BSFC = fuel mass flow ÷ brake power
When fuel flow is in kg/s and power is in kW:
BSFC (kg/kWh) = ṁ × 3600 ÷ P
Thrust Specific Fuel Consumption
TSFC = fuel mass flow ÷ thrust
When fuel flow is in kg/s and thrust is in N:
TSFC (kg/N·s) = ṁ ÷ T
Helpful Derived Relationships
Thermal efficiency ≈ 3.6 ÷ (BSFC × LHV) with BSFC in kg/kWh and LHV in MJ/kg.
Propulsive efficiency ≈ (T × V) ÷ (ṁ × LHV) when thrust, speed, fuel flow, and heating value are known.
Projected fuel used = ṁ × time, after converting time to seconds.
How to Use This Calculator
- Select BSFC for engines rated by shaft power, or TSFC for engines rated by thrust.
- Enter fuel flow and choose the matching unit. If you use volume units, keep density accurate.
- Enter power or thrust, then choose the correct unit for that output.
- Add lower heating value when you want efficiency estimates.
- Optionally add speed, duration, and fuel price to estimate distance, fuel use, and operating cost.
- Press calculate to display results above the form, export reports, and inspect the Plotly graph.
FAQs
1) What does specific fuel consumption measure?
It measures how much fuel a machine needs to produce useful output. BSFC relates fuel to shaft power. TSFC relates fuel to thrust. Lower values usually indicate better fuel economy under similar operating conditions.
2) When should I use BSFC instead of TSFC?
Use BSFC for engines, generators, and dyno-tested machines that deliver mechanical power. Use TSFC for turbojets, turbofans, rockets, or any propulsion system where thrust is the main rated output.
3) Why do density and fuel type matter?
Volume flow rates such as liters per hour must be converted to mass flow before calculating specific fuel consumption. Density handles that conversion. Fuel type also changes heating value, which affects the estimated efficiency outputs.
4) Is lower specific fuel consumption always better?
Usually yes, but compare values at similar load, speed, altitude, temperature, and mixture settings. A lower figure under one operating point may not stay lower when conditions or equipment tuning change.
5) Can this calculator handle volumetric fuel flow?
Yes. Choose L/h, L/min, or US gal/h, then provide a realistic density. The calculator converts the entered volume rate into mass flow and uses that mass flow in all subsequent formulas.
6) Why is speed optional?
Specific fuel consumption itself does not require speed. Speed is included for useful extras, such as projected distance, fuel per 100 kilometers, and propulsive power or efficiency in thrust-based operating conditions.
7) How accurate are the efficiency estimates?
They are good engineering approximations when the heating value, fuel flow, thrust, speed, and power data are accurate. They are not a substitute for full cycle analysis, corrected test data, or certified engine maps.
8) What is a good BSFC or TSFC value?
There is no single universal target. Piston engines, turbines, rockets, and marine engines operate in different ranges. Compare against manufacturer data, tested baselines, and matching duty cycles for a meaningful judgment.