It can vary with the particular type of snake, but generally you want a cage with a length of 2/3 of that of the snake and then approximately half of that. If its an arboreal species like a tree boa, then obviously, more attention needs to be paid to height than floor space.
as said it does depend on the size of the snake but you can build the for cheap and go for the biggest you can fit my boas are gonna have atleast a 4x8x4 encloser but I may go bigger they have no restriction in the wild so why confine them in your house
I've been told that theh length of the tank should be the same length as the adult snake while the width would be half the size, but then I've read that you can keep a King Snake in a 20g for life which doesn't make sense.
It really depends on the snake. Length-of-snake guidelines are a good place to start, but then you have to take into account the species of snake: how nervous is it; how active is it; arboreal or terrestrial...things like that.
You'd probably get a better answer if you told us what kind of snake you're talking about.
The bigger the better. I hate people who keep their big snakes in these tiny enclosures and say that its fine. Every few years, the minimum cage size gets smaller for some species. Give them space and they will love it.
Some of the best python and boa breeders in the country all agree that the animal sould not be able to go all around the tank and touch head to tail.
Therefore a cage that is 4' long and 2' wide SHOULD be able to house a snake that is 10', although IMO that size cage is "OK" for up to an 8' max.
This is just a GENERAL guidline though because very heavy bodied snakes would need more floorspace.
Normally boa cages are sold at the 4'x2'x18" size, which is just wrong IMO since the majority of these anomals will eventually obtain a size far too large for these cages.
Of course I have been to a couple of kingsnke breeders facilities and they house even thier adult snakes in small rack cages that are the size of a small to medium sweater box so who knows...LOL!!
The bigger the better. I hate people who keep their big snakes in these tiny enclosures and say that its fine. Every few years, the minimum cage size gets smaller for some species. Give them space and they will love it.
The minimum cage size gets smaller for some species because keepers out there are realizing that in captivity, some species benefit from the security of smaller enclosures. Among these species are borneo/blood pythons, ball pythons, angolan pythons, etc.
On the flip side, species like burms, boas, and retics need a proportionally larger enclosure than the smaller boids I listed above.
Its wrong to make a global statement like that without knowing what you're talking about.