Thrust-specific fuel consumption is the fuel mass flow divided by the net thrust: TSFC = ṁf ÷ F. It is the standard efficiency metric for jet, turbofan and ramjet engines. Modern high-bypass turbofans run roughly 0.50–0.60 lb/(lbf·h), or 14–17 g/(kN·s), at cruise.

How do I convert TSFC units?

1 lb/(lbf·h) = 28.3255 g/(kN·s) = 28.3255 mg/(N·s). kg/(kgf·h) has the same number as lb/(lbf·h), and 1 kg/(daN·h) = 27.7778 g/(kN·s). Example: 0.55 lb/(lbf·h) = 15.58 g/(kN·s).

How is TSFC related to specific impulse?

Specific impulse is the inverse: Isp (s) = 1 ÷ (TSFC × g₀) with TSFC in kg/(N·s) and g₀ = 9.80665 m/s², or Isp = 3600 ÷ TSFC in lb/(lbf·h). A turbofan at 0.55 lb/(lbf·h) has an Isp of about 6,545 s; a LOX/LH₂ rocket at 450 s corresponds to 8.0 lb/(lbf·h).

What is the Breguet range equation?

For a jet: R = (V ÷ (g·c)) × (L/D) × ln(Wi ÷ Wf), with c the TSFC in kg/(N·s). Endurance is E = (1 ÷ (g·c)) × (L/D) × ln(Wi ÷ Wf). For a propeller aircraft: R = (ηp ÷ (g·cP)) × (L/D) × ln(Wi ÷ Wf), with cP the PSFC in kg/J. They assume constant speed, L/D and SFC.

Why does TSFC change with altitude and speed?

TSFC rises with flight Mach number because ram drag reduces net thrust while fuel flow stays high, which is why cruise TSFC is much higher than sea-level static TSFC. Cold air at altitude improves the cycle, and higher bypass ratio lowers TSFC.

Specific Fuel Consumption Calculator

TSFC = fuel flow ÷ thrust; PSFC = fuel flow ÷ shaft power. Get the result in g/(kN·s), lb/(lbf·h), kg/(daN·h) and Isp seconds (or g/kWh and lb/(hp·h)), then estimate fuel burn and Breguet range and endurance.

Engine Parameters

Calculation Mode

TSFC: fuel flow ÷ net thrust.

Fuel Flow Rate

Net Thrust

Illustrative examples

Mission estimate (optional)

Uses the SFC above. Breguet assumes constant speed, L/D and SFC.

Flight time (h)

Lift / drag (L/D)

Cruise speed (knots TAS)

Start weight

End weight (same unit)

Result

Enter fuel flow and thrust (or power) values to compute SFC.

TSFC — g/(kN·s) —

Unit	Value

Fuel flow

—

Thrust

—

Car, truck, marine or generator engine on a dynamometer? Use the brake-specific fuel consumption (BSFC) calculator for g/kWh, lb/(hp·h), fuel flow in L/h or gal/h, injector sizing and brake thermal efficiency.

Typical TSFC by engine type

Representative ranges; the actual value depends on Mach number, altitude and throttle. Isp = 3600 ÷ TSFC in lb/(lbf·h). Rocket rows are converted from Isp.

Engine / condition	lb/(lbf·h)	g/(kN·s)	Isp (s)
High-bypass turbofan, cruise	0.50–0.60	14.2–17.0	6,000–7,200
High-bypass turbofan, sea-level static	0.28–0.40	7.9–11.3	9,000–12,857
Low-bypass military turbofan, dry	0.65–0.90	18.4–25.5	4,000–5,538
Turbojet, dry	0.75–1.10	21.2–31.2	3,273–4,800
Afterburning turbofan / turbojet, wet	1.70–2.50	48.2–70.8	1,440–2,118
Rocket, LOX/RP-1 (Isp ≈ 310 s sea level)	11.6	328.9	310
Rocket, LOX/LH₂ (Isp ≈ 450 s vacuum)	8.0	226.6	450

TSFC and PSFC unit conversions

1 lb/(lbf·h)	= 28.3255 g/(kN·s) = 28.3255 mg/(N·s) = 1 kg/(kgf·h) = 0.10197 kg/(N·h)
1 g/(kN·s)	= 0.035304 lb/(lbf·h) = 0.036 kg/(daN·h)
1 kg/(daN·h)	= 27.7778 g/(kN·s) = 0.98066 lb/(lbf·h)
Isp	= 1 ÷ (TSFC [kg/(N·s)] × 9.80665) = 3600 ÷ TSFC [lb/(lbf·h)] seconds
1 lb/(hp·h)	= 608.277 g/kWh = 0.168966 mg/J (PSFC / BSFC)

Formulas and worked example

TSFC = ṁ_f ÷ F (kg/(N·s)); PSFC = ṁ_f ÷ P (kg/J). Multiply kg/(N·s) by 10⁶ for g/(kN·s) and kg/J by 3.6 × 10⁹ for g/kWh.
Jet Breguet range R = V ÷ (g·c) × L/D × ln(W_i ÷ W_f); endurance E = 1 ÷ (g·c) × L/D × ln(W_i ÷ W_f).
Propeller Breguet range R = η_p ÷ (g·c_P) × L/D × ln(W_i ÷ W_f).

Example: a turbofan burns 1,500 kg/h at 25 kN cruise thrust. TSFC = (1500 ÷ 3600) ÷ 25,000 = 1.6667 × 10⁻⁵ kg/(N·s) = 16.67 g/(kN·s) = 0.5884 lb/(lbf·h), Isp ≈ 6,118 s. At 450 kt (231.5 m/s), L/D 17 and a weight ratio of 70,000 ÷ 56,000, range = 231.5 ÷ (9.80665 × 1.6667 × 10⁻⁵) × 17 × ln 1.25 ≈ 5,373 km (2,901 nmi) and endurance ≈ 6.45 h.

Summary

Specific fuel consumption (SFC) measures how much fuel an aircraft engine burns for the thrust or power it delivers. Thrust-specific fuel consumption (TSFC) is the jet and turbofan metric; power-specific fuel consumption (PSFC) is used for turboprop, turboshaft and piston aircraft engines. Lower SFC means better efficiency. TSFC is the inverse of specific impulse (Isp = 1 ÷ (TSFC × g₀)) and sets range and endurance through the Breguet equations. For car, truck, marine and generator engines use the brake-specific fuel consumption (BSFC) calculator.

How it works

Select TSFC (jet / turbofan) or PSFC (turboprop / piston).
Enter the fuel flow (kg/h, lb/h, g/s or kg/s) and the net thrust (kN, lbf) or shaft power (kW, hp).
Read the SFC in all common units; for TSFC also the equivalent specific impulse in seconds.
Optionally enter flight time, cruise speed, lift-to-drag ratio and start and end weights to get fuel burned and Breguet range and endurance.
Compare with the typical ranges by engine type below.

Use cases

Convert TSFC between g/(kN·s), mg/(N·s), lb/(lbf·h), kg/(kgf·h) and kg/(daN·h).
Relate jet TSFC to rocket specific impulse (Isp) for propulsion coursework.
Estimate cruise range or endurance from TSFC, L/D and fuel fraction with the Breguet equation.
Evaluate turbofan efficiency in preliminary aircraft design.
Check turboprop or piston aircraft PSFC and propeller-aircraft range.
Validate engine test or flight-test data against typical values.

Frequently Asked Questions

Last updated: 2026-10-09 · Reviewed by Nham Vu