An index based on a graphical approach is developed to compare the amenability to washing of several coals and evaluate coal washability characteristics. A curve labelled the CM-curve, which may be viewed as the complement of M-curve, is introduced. For each coal sample the associated M-curve and CM-curve are normalized, using the overall ash content of the coal sample, such that different coals can be evaluated using the same base. At a particular cumulative mass the abscissa distance between the two normalized curves has a maximum value that can be used as an index for evaluating washing characteristics and comparing amenability to washing of several coals. The index varies between zero and one. The larger the index the easier the coal is to wash. The proposed index is simpler and superior to existing indices. Practical data are used to illustrate the index developed.