A method for calculating the degree of mineral matter liberation by the sink-float separation data of coal was studied. The mineral composition was estimated by norm calculation using the results of elemental analyses of sink-float separated coals. The content of the inherent ash from the lowest density fraction and the minimum limit of the locked particle rate from the highest density fraction were also estimated, and the degree of the maximum mineral matter liberation (MLmax) was calculated from these results. The MLmax can be easily measured by carrying out sink-float separation at only two density points, and by measuring the weight, ash content, and ash element of these three density fractions. Because coal properties such as particle size and mineral composition are well reflected in the value, the MLmax is useful as a substitute index of the true degree of liberation. (C) 2003 Elsevier Ltd. All rights reserved.