There are a lot of opinions with this topic. Everybody has one and I believe there isn't a definitive answer. Personally it depends on the snake. I have a very large female (4300gm), and she is in a large enclosure and I also have a small male (1200gm) it seems silly to make a blanket statement that as 3 year olds they should be housed in a ___.

I go by the width plus the length should not be much shorter than the snake occupants. So a 30x24 would be fine for an animal of 54 inches perhaps 56 at the most. I know some would say the circumference rather than 2 sides I usually go with a bit bigger myself, as that the diagonal length allows the snake to stretch fully (mostly anyway).