Dragon Glass DFG10-R09M Reflective Fireglass, 10 lb, Crystal Glass will not melt, degrade or produce toxic fumes Glass size -1/2" or 12-20 mm 0.125 cu. Ft. Bag, coverage area .47 sq. Ft Rectangular fireplace/ fire pit (length x depth x glass Height)/ 19 = glass (lbs.) Round fireplace/ fire pit (diameter x diameter x glass Height)/ 24 = glass (lbs.)