it is 3ft long 14inch tall and 2ftwide
That should do for along time but when your beardie gets older raise the height to like 2 feet and more length is preferable.
according to my brother, that size should be fine. he has a bearded dragon as well. however, the size of your bearded dragon will depend on the size of your tank as well. so the bigger the tank, the bigger the bearded dragon.