How much soil is needed?

if i wanted to flower a single plant (actually 3) to have the ability to grow 1/4lb a piece, how much room in soil would the roots need? is this possible by putting 3 plants together in a 20 gallon bucket? yea we've all heard u should keep your plants seperate. some people feel differently.

is there a dirt amount to yield ratio anyone is familiar with?


thanks

if you want 1/4 lb per plant 5 gal growbags are good