Is there a minimal tank/cage size requirement for reptile?

I know this is my standard answer, but it depends on the species. Weather it is arboreal or semi arboreal, very active or not, ect... The standard rule with snakes is the cage should be at least 2/3 as long as the snake. I think you want the length x width of the enclosure to equal the length of the snake. But if it is an arboreal species, you have to take height into account to. Most lizards need a bit more space, as they tend to be more active. The larger species of monitors and tegus really need large enclosures. Bearded dragons, blue tongued skinks, uromastyx, frilled dragons, etc... even though smaller, still need moderate sized enclosures so they have space to roam, and so that it is possible to provide appropriate basking temperatures as well as cooler areas so the animals can thermoregulate properly.