Brake Specific Fuel Consumption Calculator
Calculate brake specific fuel consumption (BSFC) — how much fuel an engine burns per unit of power produced. Enter the fuel mass flow rate and the brake power output to see the BSFC, a key measure of engine efficiency.
Formula
BSFC = Fuel Mass Flow Rate ÷ Brake Power
- BSFC measures how much fuel an engine consumes to produce a given amount of power — the engine equivalent of fuel economy.
- Dividing fuel mass flow (kg/h) by brake power (kW) gives kg/kWh; multiplying by 1000 gives the common g/kWh figure.
- A lower BSFC means the engine extracts more work from each gram of fuel, so it is more efficient.
- Efficient modern diesel engines reach roughly 200 g/kWh near their best operating point; petrol engines are typically higher.
- BSFC varies across the engine's speed and load map, so a single value reflects one operating condition.
20 kg/h fuel, 75 kW power
Inputs
- Fuel Mass Flow Rate: 20 kg/h
- Brake Power Output: 75 kW
BSFC = 20 ÷ 75 = 0.267 kg/kWh = 267 g/kWh at this operating point.
Frequently asked questions
What is brake specific fuel consumption?
It's the rate of fuel an engine burns divided by the brake (output) power it produces, measuring how efficiently fuel is converted into useful work.
Why is a lower BSFC better?
A lower BSFC means less fuel is needed for each unit of power, so the engine is more efficient and cheaper to run.
What units is BSFC measured in?
Commonly grams per kilowatt-hour (g/kWh), or pounds per horsepower-hour (lb/hp·h) in imperial units. This calculator outputs g/kWh and kg/kWh.
Does BSFC stay constant?
No. It changes with engine speed and load. Engines have a 'sweet spot' of minimum BSFC, often shown on a fuel-consumption map.