Regression analysis is used to develop equations for calculating fusion temperatures of coal ash from chemical composition, based on 1250 analyses of ash from both eastern and western coal. Standard errors for the equations are generally less than 50°F (27°C), which is the analytical tolerance of the ash fusion temperature measurements. Equations are given for eastern, western, and combined eastern and western coals. These equations: (1) provide a technique for calculating ash fusion temperatures from the chemical composition of the ash; (2) provide a method for calculating the ash fusion properties of coal blends; and (3) provide an improved understanding of the effect, significance, and interactions of ash elements with respect to the thermal properties of coal ash.