The above posts are spot on but they are not hardfast rules.

As people have said, you can get away with a bigger enclosure for a smaller snake if you provide ample cover.

I kept a few of my snakes in 41 qt tubs from 150g - 500g and none of them missed a meal or showed signs of stress.
I gave 4 or 5 appropriate sized hides, several fake plants, and several half logs and branches to fill the space. No problem.

Funny enough, for my own space issues I downgraded them all to 32 qt tubs until they really need the space. They hide in 1 of 2 6" by 6" spots nearly 90% of the time. Lots of space is simply overkill for ball pythons.

Remember, this is where they would live if they had the choice: