What reptile for a 4'8" L x 18" W x 3.5' H

[DennisM]

I was more using it as a reference for larger constrictors but me personally, i would try and give any snake the ability to at least stretch out 3/4 of its body. Would be like us being crammed in a closet lol. Thinner snakes could obviously get by with a thinner cage.

yes, like you said, "a general rule", not the law. thicker snakes require deeper cages. thinner snakes of the same length can do fine in narrow cages. I think most adult king\milk will do well with a 36x18 floor space, though I would provide larger species (Honduran for example) with 36x24 or preferably 48x24. kings and milks will climb, but I don't feel it's a requirement as they are largely terrestrial.

as always, know the animals needs.