The marijuana growers bible by Jorge Cervantes says this about plant life and pot size:
2-6 weeks - 4 inch pot
6 weeks to 3 months - 3 gallon pot
3-8 months - 5 gallon pot
I use three gallon pots and they seem to be big enough for me. Hope this helps.
I use 5gal. pots for all stages of growth with my plants. They allow the rootball to develop enough not to cause the plants to become rootbound. However a 10gal. is better because you have more space of course. But if space is ann issue go with a 5gal. youll be happy you did. No need to transplant.