BSFC Calculator

This BSFC calculator works out brake specific fuel consumption, the measure of how much fuel an engine burns for each unit of power it produces at the crankshaft. Enter the volumetric fuel flow, the fuel density and the brake power output, and the calculator converts the flow to a mass rate, divides it by the power, and returns the BSFC in grams per kilowatt hour, the fuel mass flow in kilograms per hour, the engine thermal efficiency, and the same BSFC in the imperial pounds per horsepower hour that many engine builders still quote. BSFC is the fairest single number for comparing engines of different sizes, because it strips out capacity and rates the engine purely on how efficiently it turns fuel into work. A lower figure is better. The defaults describe a petrol engine making 100 kW while drinking 30 litres an hour of fuel at 745 grams per litre, which lands around 223 grams per kilowatt hour and a thermal efficiency near 37 percent, typical of a modern petrol engine at a good operating point. Set the density to about 832 grams per litre for diesel, and adjust the lower heating value if you want the efficiency figure to match a specific fuel. Use it to compare engines, track a tune on a dyno, or turn a fuel flow reading into an efficiency you can reason about.

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BSFC is fuel mass flow divided by brake power. Thermal efficiency uses the lower heating value you enter (43.4 MJ/kg suits petrol, about 42.7 for diesel). Figures apply to the single operating point you enter, not the whole engine map. Estimate only.