# BSFC Calculator (Brake Specific Fuel Consumption)

URL: https://speedycalculator.com/calculators/everyday-life/bsfc/
Last updated: 2026-10-25

> The BSFC calculator finds an engine's brake specific fuel consumption – fuel burned per unit of power output – in g/kWh and lb/hp·h, and its thermal efficiency for petrol, diesel, LPG, methane or kerosene.

## Inputs

- Fuel flow rate (g/s, kg/h, lb/h)
- Power from
- Power (kW, hp, W)
- Torque (N·m, lbf·ft)
- Engine speed (rpm)
- Fuel

## Results

- Power used
- BSFC
- Thermal efficiency

## Formula

```
BSFC = fuel flow ÷ power
Power = torque × angular speed (optional)
Efficiency = 1 ÷ (BSFC × fuel energy content)
```

## Explanation

Brake specific fuel consumption is the standard way to compare how efficiently engines turn fuel into work, independent of size. Good modern petrol engines reach about 230–250 g/kWh at their best point, diesels 200 g/kWh or less. The lower the BSFC, the higher the thermal efficiency.

### How to use the BSFC Calculator

- **Fuel flow rate**
- **Power from**
- **Power**
- **Torque**
- **Engine speed**
- **Fuel**
- Every result field is editable: type into **BSFC** and **Fuel flow rate** plus every other field update to match.

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Enter the fuel flow and the power output (or the torque and rpm), and choose the fuel. The calculator divides fuel flow by power and converts BSFC to efficiency using the fuel's lower heating value.

### Tips

- Use your own measured figures – fuel economy, speed and prices vary a lot with driving style, traffic, load and season.
- Pick the unit in each field's menu (miles or kilometres, mpg or L/100 km); the calculator converts everything for you.
- Fill up to the brim twice and divide the distance by the fuel added to measure real fuel economy.
- For vehicle modifications, treat results as a starting point and confirm with the parts maker or a professional mechanic.

### Common mistakes to avoid

- Mixing US and imperial (UK) gallons – a UK gallon is about 20% bigger.
- Using the advertised fuel economy instead of real-world figures.
- Forgetting tolls, parking and wear and tear when comparing driving with public transport.

### Inputs explained

FieldWhat to enterFuel flow rateUnits: g/s, kg/h, lb/hPower fromChoose one: Power value, Torque and rpmPowerUnits: kW, hp, WTorqueUnits: N·m, lbf·ftEngine speedIn rpmFuelChoose one: Gasoline / petrol, Diesel, LPG, Methane (natural gas) …

### What each result means

- **BSFC** = [Fuel flow rate]÷([Power used]÷1000)×3600
- **Thermal efficiency** = 100÷([BSFC]×[Fuel])

### Example values

How the main result changes when **Fuel flow rate** changes and everything else stays at the example values above:

Fuel flow rate (g/s)BSFC (g/kWh)2.51203.7518052406.253007.536010480

## Worked example

Inputs — Fuel flow rate: 5 g/s; Power from: Power value; Power: 75 kW; Torque: 250 N·m; Engine speed: 3,000 rpm; Fuel: Gasoline / petrol.

Results — Power used = 75 kW; **BSFC = 240 g/kWh**; Thermal efficiency = 34.5 %.

## FAQ

**What is a good BSFC?**
About 200–210 g/kWh for large diesels, 230–260 g/kWh for good petrol engines at their best operating point.

**How do I convert g/kWh to lb/hp·h?**
Divide by 608.3. 250 g/kWh = 0.41 lb/hp·h.

**Why does BSFC change with load?**
Engines are most efficient near full load at moderate rpm; at light load pumping and friction losses dominate.

**What formula does the BSFC Calculator use?**
BSFC = fuel flow ÷ power.