I have found as a "rule of thumb" is as high and as wide as the plant will get, allow for roots. like if the plant is expected to get three feet tall, then a three foot container, or two feet wide a two foot container at width. But, this is just a rule of thumb, cause i have grown 5+ foot plants in like a less than five gallon container. that was before i got my MMJ recomendation, now i cant seem to grow over a four foot plant in a 15 gallon container! Go figure. (but the grow season is young yet)
