The estimation of in situ coal density has been the subject of extensive research due to its importance for coal reserve estimation. However, despite decades of studies, a universal method for density estimation that can be applied to all coal deposits still does not exist. Traditional ash-based methods are inaccurate because ash is a combustion product that does not contain the volatile mineral components which are lost upon combustion. Coal is composed of three primary constituents: organic macerals, inorganic mineral matter, and moisture. Understanding the properties of the mineral matter is particularly critical for accurate density estimation. The method described herein improves the accuracy of density estimates by first estimating the mineral matter percentage of each sample using only ash and specific energy analyses, both of which are performed on the large majority of exploration samples. A least-squares hyperbolic formula is derived from the dry coal and mineral properties in order to estimate the dry sample density. The formula accepts two in situ moisture percentages, for both coal and rock, in order to estimate in situ density for coal and other lithologies. This method has several advantages over existing techniques. It is valid for all values of ash, with no loss in accuracy outside a limited range. The scatter caused by mineral volatiles is reduced, resulting in a much higher correlation coefficient. Coal and mineral densities derived from the formula may also provide insight into the coal maceral and mineral types present within a project, as well as changes in mineralogy with ash content. (C) 2016 Elsevier B.V. All rights reserved.