perimeter answers to where I obtained the 2x length
http://www.anapsid.org/enclsize.html
Snakes
Dimension Total LengthMinimum length (side to side): 3/4 of total lengthMinimum depth (front to back): 1/3 of total lengthMinimum height: Terrestrial/Fossorial: 3/4 of total lengthArboreal/Scansorial: 1 x total length, max 6-8 ft
http://www.applegatereptiles.com/art...ookhousing.htm
Size of enclosure: Avoid extreme sizes. If an enclosure is too large, a snake can become "lost in it" making it generally difficult to monitor its overall health and behaviors. A snake in an enclosure that is too large and poorly designed may also stay at one end, hidden, and not venture forth to seek out food items. On the other hand, too small an enclosure will result in a snake that will be cramped, lying in its own feces, and unable to utilize heat gradients. A small cage will also "foul" faster and be more difficult to keep clean and properly ventilated. The proper cage is one where if the snake were to crawl around the perimeter, it would cover approximately half the perimeter measurement, with a reasonable width to length ratio (no long skinny cages!) A good general rule is a width approximately one third of the length of the snake. Although milk snakes will occasionally climb, tall cages are not essential for their maintenance. A standard 5 gallon vivarium will not be large enough for maintaining a hatchling snake up to a year. A standard 20 gallon high or 15 gallon low vivarium (12" wide x 24" long) will be a suitable minimum size for all but the largest subspecies of adult milk snakes. Large subspecies such as Honduran milk snakes will require commercial enclosures at least 30 inches long.
http://www.worldofballpythons.com/python-regius/care-sheet/
Enclosure
There are two ways to house your snake. The first, and most popular way is in a terrarium. The second method (used more commonly by breeders) is in a rack system.
The size of your enclosure should not exceed one and half times the length of your snake and should not be less than two thirds the length of your snake. In a terrarium, I prefer to go a little larger so that the enclosure is not too cluttered.
There are many who believe that there is no maximum size to the enclosure - provided the snake has plenty of hides and ample foliage.
to list a few not saying racks are a bad thing but how do you determine the appropriate size rack if that is your choice? I am just curious If my husband and I get into breeding we want to have the best possible housing for our breeders as we would keep things small and they would still be like pets to us.