In this study, a relation for calculating the Bond grindability by the sink-float test data of coals was studied. Primarily, sink-float tests for three coal samples were made. Secondly, the cumulative weight and ash content of the floating fraction were determined for three different coal samples in all relative densities tested. Then, grindability of the coal samples were determined for its constituent specific gravity fractions. The relationships between the Bond grindability and relative densities have been stated as simple polynomial equations and the calculated values from equations have been compared with the experimental results. Finally, the float-sink test results can be stated by simple equations relating to the Bond grindability value. The Bond grindability (G(bg)) was easily determined by carrying out sink-float separation.