Still confused about container size needed

[tulsanurse1]

Is a container size W20.5 X H12.0 overkill for a tomato plant? I purchased it to put 2 indeterminant plants in but now will only be planting 1 in it instead, due to overcrowding. What ideally is the smallest size container one could use for planting on BeefSteak tomato plant in. No sense spending all that money on the containers if I don't ultimately need it. Sorry for my confusion. I appreciate all the feedback but still a little a little confused and just want to do this right economically.