Big ben is the name given to the massive bell inside the clock tower that weighs 13.7 tonnes stands 7.2 ft ( 2 .2 meters) tall and has a diameter of 8.9 ft ( 2.7 meters) . The bell hammer weighs 200 kgs . Each dial on this clock is seven meters in diameter and numbers are approximately 60 cm long . The hour hand is 9.2 feet long ( 2.8 m ) in length the minute hand is 14 feet ( 4.3 m ) . Each clock dial is illuminated by 28 energy efficient bulbs at 85 watts each bulb has a lifetime of 60, 000 hours . In june 2012 this clock tower was renamed as the elizabeth tower to mark the diamond jubilee of elizabeth 2 and stands 315 ft ( 96 meters) tall with 11 floors .