The tubers can get quite large for each plant. But the pot will also constrain it. I would go with 1 plant in a 6 inch diameter and 6 inch deep pot. Anything smaller will probably be an unhappy plant. But you could probably push 2 or 3 plants in that sized pot, but they will not do well.
I grow them in the ground and dig up/store/replant the tubers.
