Fuel Efficiency Mass Converter

This converter is for the energy a fuel holds per unit of mass, its specific energy or heating value, in J/kg, kJ/kg, cal/g or Btu/lb. Diesel holds about 43,000 kJ/kg, petrol (gasoline) about 44,000 and natural gas about 50,000.

It also converts the inverse: the mass of fuel per unit of energy. Engine makers use this as the specific fuel consumption, in g/kWh or lb/(hp·h). A modern diesel engine uses about 200 g/kWh at its best.

How to convert energy per mass

Type a value into any field, and every other unit is calculated at once. For example, diesel at 43,000 kJ/kg:

1. In Btu/lb: multiply by 0.429923.

   43,000 × 0.429923 = 18,490 Btu/lb

2. In kcal/kg: a kcal/kg is the same as a cal/g.

   43,000 kJ/kg = 10,270 cal/g = 10,270 kcal/kg

Specific fuel consumption converts the same way: 200 g/kWh is 0.329 lb/(hp·h).

Common conversions

The Btu and calorie values are the International Table (IT) units.

Energy per mass units

• Joule / kilogram (J/kg): The amount of energy produced per kilogram in joules.
  Conversion Factor: 1 J/kg = 1 J/kg (Base Unit)

• Kilojoule / kilogram (kJ/kg): The energy produced per kilogram in kilojoules.
  Conversion Factor: 1 kJ/kg = 1,000 J/kg

• Calorie / gram (cal/g): The energy produced per gram in calories.
  Conversion Factor: 1 cal (IT) / g = 4,186.8 J/kg; 1 cal (th) / g = 4,184 J/kg

• Btu (IT) / pound (Btu/lb): The energy produced per pound in British Thermal Units.
  Conversion Factor: 1 Btu (IT) / lb = 2,326 J/kg; 1 Btu (th) / lb = 2,324.44 J/kg

The following are reciprocal units, revealing the mass required to produce a certain amount of energy:

• Kilogram / joule (kg/J): The mass required to produce one joule of energy in kilogram. kg/J is the reciprocal value of J/kg.
  Conversion Factor: 1 kg/J = 1 / (J/kg)

• Kilogram / kilojoule (kg/kJ): The mass required to produce one kilojoule of energy in kilogram. kg/kJ is the reciprocal value of kJ/kg.
  Conversion Factor: 1 kg/kJ = 1 / (kJ/kg)

• Gram / calorie (g/cal): The mass required to produce one calorie of energy in gram. g/cal is the reciprocal value of cal/g.
  Conversion Factor: 1 g/cal = 1 / (cal/g)

• Pound / Btu (lb/Btu): The mass required to produce one British Thermal Unit in pounds. lb/Btu is the reciprocal value of Btu/lb.
  Conversion Factor: 1 lb/Btu = 1 / (Btu/lb)

• Pound / horsepower / hour (lb/hp/h): The mass required to produce one horsepower-hour of energy in pounds.
  Conversion Factor: 1 lb/hp/h = 5,918,352.5016 / (J/kg)

• Gram / kilowatt / hour (g/kW/h): The mass required to produce one kilowatt-hour of energy in gram.
  Conversion Factor: 1 g/kW/h = 3,600,000,000 / (J/kg)