Derived and discussed are empirical relationships that describe dependencies of the true density and yield of coal chars on carbonization temperature in the 550-1000 degrees C range. They include formulae for the determination of mass and true density changes with temperature for both organic matter and mineral matter in the coal chars. The relationships are based on results of investigations of laboratory-scale made coal chars under comparable conditions to industrial-scale carbonization processes and, therefore, should also be valid for coke products. Additionally, technological parameters such as a bulk density of coal blend and specifics of grinding process are found not to influence significantly the true density and yield of the coal chars. (C) 2000 Elsevier Science Ltd. All rights reserved.