During determination of volatile matter in coking coal a solid reside in left, comprising of fixed carbon and mineral matter. The solid residue that is the coke bead is viewed horizontally at the same level of the eye. It will be observed that the top surface of the bead has developed some amount of swelling. This swelling is compared with standard chart indicating there quantum of swelling and a number indicating swelling index. Swelling index varying between 2.-5 is ideal for coke manufacturing. The high swelling coal is not charged for coke making as it would create unnecessary pressure on the side wall of the oven will also produce a coke porous structure.