While chemistry provides ways of calculating the heating value of a certain amount of a substance, there is a difference between this theoretical value and its application to real coal.
The grade of a sample of coal does not precisely define its chemical composition, so calculating the coal's actual usefulness as a fuel requires determining its proximate and ultimate analysis (see "Chemical Composition" below).
Chemical composition of the coal is defined in terms of its proximate and ultimate (elemental) analyses.
The parameters of proximate analysis are moisture, volatile matter, ash, and fixed carbon.
Elemental or ultimate analysis encompasses the quantitative determination of carbon, hydrogen, nitrogen, sulfur and oxygen within the coal.