mogie is right, it depends on type of grow.....also, space available, lighting, temps....lots of variables....another to consider is the strain. Some strains are better than others at producing good yield from smallish containers....I like to use 1 gallon for Apollo 11, for example. A good "default" size, IMO, would be a two gallon....not too small.... (basically a multi strain, smallest size container to get decent bud harvest from most types of ganja.)
You could grow monsters in a five gallon under optimum conditions (outdoors.)
Obviously, another variable you can control is the amount of time you veg...If you flower early, the girls won't need as much room to thrive!