The amount of energy contained in coal is known as the heating value of the coal. It is measured in Btu/lb. For gas and other volatile fuels, heating value is expressed in Btu/cu ft at a standard temperature and pressure. A Btu
is the amount of heat required to raise the temperature of 1 pound of mass (0.45 kg) of pure water by 1 degree Fahrenheit (0.55 degree Celsius) at atmospheric pressure.
Different types of coal from different areas of the country have different heating values. Bituminous coal has a higher heating value than lignite. Therefore, there is more energy in each pound of bituminous coal than there is in each pound of lignite.