Depends on the overall size of your plant....hence strain and vegging period...remember bigger roots bigger shoots....overall 1 foot of growth equals one gallon of soil....just to let you know home depot has 5 gallon buckets on sale for $3.00...with some holes drilled in the bottom they make a great cheap pot.
Indica dominant strains vegged for 4-6 weeks and then flowered would be fine in 3 gallonish containers, in my experience. They work for me, anyway.