When should I move my bp into a bigger enclosure?

He's about 15 or 16 inches right now and lives in a 10 gal aquarium. How big should he be before I move him into a bigger enclosure? Also, his next enclosure will probably be a sterilite tub, so how big should the tub be after moving him from a 10 gal tank?

Generally you want 1 square foot of floor space per foot of snake. I would go with a 28 or 32 quart tub.

I have my little male normal in a 32 quart sterilite tub and he just barely weighs 300 grams. He is doing very well in this size tub.

From what I understand the size of the tub can sometimes upset some ball pythons too. I found that some snakes can get stressed from moving into a larger space. Make sure the snake has plenty of hiding spots or is secluded enough. I have an open sided rack now with four 100 gram babies i just got. Three of them are doing, great but one is very defensive about movement outside the rack. Keep an eye on his body language to see if he is stressed after making the switch.