There are two general guidelines that I have always heard people use:
1) 1 square foot of floor space per 1 foot of snake length. That would mean that a 4' X 2' enclosure could hold up to an 8 foot snake.
2) The length + width of the enclosure should be greater than the length of the snake, in which case, the same 4' X 2' enclosure would only be suitable for a snake up to 6 feet.
Since my boas are smaller species I haven't had to deal with caging for a large boa in the 9'-11' range, but I would say, for a snake that big, the smallest enclosure that you could get away with would be something like a 6' X 2' and something like an 8' X 3' would probably be your best bet...
I agree. Ive heard a rule that a cage should be no less than half the length of the snake. My female is close to 6ft and is in a 4x2 cage. She seems to have plenty of room but when she gets bigger, i could see myself making a 5x2 or 6x2.
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