BSFC Calculator

Calculate brake specific fuel consumption from fuel flow rate and brake power output. BSFC = fuel mass flow rate ÷ brake power, reported in lb/hp·hr and g/kWh.

Quick Facts

Formula
BSFC = fuel mass flow rate ÷ brake power
Lower BSFC means the engine burns less fuel to make the same power.
Typical range
≈0.45-0.60 lb/hp·hr for gasoline engines
Well-tuned diesels are usually more efficient, around 0.30-0.40 lb/hp·hr.

Your Results

Calculated
BSFC (Imperial)
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lb of fuel per hp per hour
BSFC (Metric)
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Grams of fuel per kW per hour
Fuel flow (converted)
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Equivalent mass flow rate
Efficiency rating
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Vs. typical engines of this type

Ready

Enter fuel flow rate and power output, then press Calculate.

Understanding Brake Specific Fuel Consumption (BSFC)

Brake specific fuel consumption measures how much fuel an engine burns to produce a given amount of power over a given time. It is the standard way engineers compare the efficiency of engines regardless of their size: a bigger engine will naturally burn more fuel in absolute terms, but BSFC normalizes that by the power it actually delivers.

The formula

BSFC is defined as the fuel mass flow rate divided by the brake power output:

  • BSFC = ṁ / P, where ṁ is the fuel mass flow rate (mass of fuel consumed per hour) and P is the brake power measured at the crankshaft or dynamometer.
  • In imperial units this is usually expressed in pounds per horsepower-hour (lb/hp·hr): fuel flow in lb/hr divided by power in hp.
  • In metric units it is usually expressed in grams per kilowatt-hour (g/kWh): fuel flow in g/hr divided by power in kW.
  • The two units convert directly: 1 lb/hp·hr ≈ 608.3 g/kWh, since 1 lb = 453.6 g and 1 hp = 0.7457 kW.

Typical BSFC values

Naturally aspirated gasoline engines commonly run around 0.45-0.60 lb/hp·hr at a steady operating point. Turbocharged or supercharged gasoline engines often run a little higher because of fuel enrichment used to control combustion temperatures under boost. Diesel engines are generally the most efficient, typically around 0.30-0.40 lb/hp·hr, thanks to their higher compression ratios and lean, unthrottled operation. These are rule-of-thumb ranges, not fixed limits — actual BSFC depends heavily on engine design, tuning, and the specific speed and load at which it is measured.

Why BSFC matters

Engine builders and tuners use BSFC to size fuel systems (injectors, pumps, fuel lines) for a target power level, to compare how efficiently different engines or tunes convert fuel into power, and to spot problems — a BSFC that is unexpectedly high for a given engine type often points to a rich air-fuel mixture, ignition timing that is off, or a mechanical issue. Because BSFC varies with engine speed and throttle position, meaningful comparisons should use readings taken at similar power and RPM.

Frequently Asked Questions

What is brake specific fuel consumption (BSFC)?
BSFC is the mass of fuel an engine burns per unit of brake power produced per hour. It is calculated as fuel mass flow rate divided by brake power, typically expressed in pounds per horsepower-hour (lb/hp-hr) or grams per kilowatt-hour (g/kWh). Because it normalizes fuel use by power output, BSFC lets you compare the efficiency of engines of different sizes.
What is a good BSFC value?
It depends on engine type. Naturally aspirated gasoline engines typically run about 0.45-0.60 lb/hp-hr at steady operating points, turbocharged or supercharged gasoline engines run a bit higher due to pumping and enrichment losses, and diesel engines are usually more efficient at roughly 0.30-0.40 lb/hp-hr. Lower BSFC means less fuel burned for the same power.
How do I convert BSFC between lb/hp-hr and g/kWh?
Multiply a lb/hp-hr value by about 608.3 to get g/kWh, or divide a g/kWh value by 608.3 to get lb/hp-hr. This factor comes from converting pounds to grams (453.6 g/lb) and horsepower to kilowatts (0.7457 kW/hp).
Does a lower BSFC always mean a better engine?
Lower BSFC means better thermal efficiency at that specific operating point, but BSFC varies with engine speed and load — most engines have a "sweet spot" where BSFC is lowest and it rises at idle or wide-open throttle. Compare BSFC values measured at similar power and RPM for a fair comparison.

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