In this study, limestone samples (a total of 108 sample) were collected from two limestone quarries. The collected samples were initially in the form of palm sized and they were crushed to -2.36 mm. Grinding experiments were conducted in standard HGI (Hardgrove Grindability Index) mill and Ring mill. PSD (Partide Size Distribution) analyzes were carried out for the samples ground with Ring mill. HGI test results were compared with the PSD results. A new method for the prediction of HGI of limestone samples from both of the quarries (Quarry-1 and Quarry-2) was proposed. Significant correlation (R-2 = 0.84) was obtained with D-90 size parameter. In terms of grinding energy calculations, Bond Work Index (BWI) was taken into consideration. In addition, proposed method for HGI prediction was employed to understand the possible role of microwave pre-treatment. (C) 2021 Elsevier B.V. All rights reserved.