Calorific value is the amount of heat produced by the combustion of a fuel mass, and is typically expressed in joules per kilogram. All elements considered to be fuels have a calorific value. There are two calorific values for fuels: higher and lower. Higher assumes that water vapor is totally condensed and the heat produced is recovered. Lower assumes that the water vapor is retained but not the heat. To start calculating a calorific value, you need to know the type of fuel and get its density.

Choose your type of fuel so you can determine its energy density.

Get the density from research institutions online (see Resources). Using gasoline as an example, the School of Oceanography at Washington University states that a U.S. gallon of premium gasoline has a density of 132 mega joules per gallon (132 Mj/gallon).

Convert gallons to liters by multiplying 132 by 0.266 to get 35. This is the Mega joules per liter (35 Mj/l).

Multiply 35 by 1,000 to get 35,000, equating to 35,000 kilo joules per liter (Kj/l is the unit of measurement generally used).

Divide 35,000 Kj/l by four. This assumes that one calorie equals four Joules. The result is the calorific value, which in this example indicates a U.S. gallon of premium gasoline has a calorific value of approximately 8,750 Kj/l.