The paper deals with the problem of reliable definition of heating value, volatile yield and sulfur content in coal organic matter and develops the methods of calculation evaluation of these parameters for coals with real ash content. The amendments due to mineral matter thermal decomposition are accounted. 8 power coals of Donetsk and Lvov-Volyn basins are studied having volatile yield from1 to 40% in frameworks of ash content from 10 to 40%. Calculations based on parameters defined more precisely differ from laboratory results not more than allowed laboratory test error value.