Reptiles in captivity are kept in enclosures that are suitable for keeping and raising them. These bearded dragons vivariums also known as cages, aquariums and tanks, should be big enough for your lizard. The tank must be installed with proper light and heating equipment and substrate to keep him comfortable and happy.It is important to have the enclosure ready before you bring your pet home. For an adult bearded dragon a tank four feet long by two feet wide and two feet high should be the minimum size to house it comfortably. The floor space is more important than the height of the tank for a fully grown dragon to move around with ease.