Get yourself a large utility pot so the tomato can grow properly. Otherwise it will be a losing battle and your yield will be poor. I'd use at least a 15 gallon pot, which measures about 15" in diameter and 15" high

For the big indeterminate tomatoes a 5 gallon bucket is the smallest you should go. Your 9 inch round pot would work for a single micro dwarf. A normal dwarf tomato may be happy in a 12 inch pot but would be happier and produce more tomatoes in a 14 inch or larger pot. What tomato varieties did you buy?

Whoa!! I would never try to grow an indeterminate in a 5G container!! For a plant that wants to be 6-8' tall or more, that is not nearly enough room for proper root development.

kudzu pretty much nailed it :-) 15G is about the smallest I would go with. I grow mine in 20G containers and the roots completely fill the pot by the end of the season.

A 9" pot would be small for most tomatoes. It would probably work for a small bush type tomato. I grow a lot of my tomatoes in 12" pots, and they do fine. They climb their ladders, and then they sprawl and I stake them. Now granted, some of my pots have large cracks in the bottom, so the roots grow a bit into the ground, but most of my plants stay fully in their pots. We've grown yellow pears in as small as 11" pots, and they did fine. Smaller pots will result in slightly reduced plant size, so the tomato in the 11-12" pot ends up being a bit smaller than the one in something larger. Your potted tomato, especially in a smaller pot, is unlikely to achieve the full 12' listed in the plant's information. The plants with the largest plant size to pot size ratio will dry out the fastest, and the super tall plants may end up being a bit top heavy.

I also have some larger pots/planters for tomatoes ... they still need to be watched for water and top-heaviness, though the stakes are usually contained to the pot rather than in and around the pot and across to fight the mint, haha.

I bought some of the enormous pot sizes mentioned by others; I hated them. One lives in the basement, collecting dust because it wasn't worth the return shipping to get rid of them, and the other was finally sunk in the back garden and does have a tomato in it. We filled the bottom half of that pot with garden soil (from the hole dug for it) because we didn't want to use up three plants worth of potting soil to fill the darn pot. The plant may as well be in the ground ... can't move the full pot anyways, which is half the benefit of pots.

16" pot with Shimmer tomato in it and a trellis I have for my peas that didn't get grown this year:

12" pots with Chocolate Cherry and Sun Peach:

(These are in the sprawl location with with the mint to their right.) These plants are the same age ... our Chocolate Cherries are just ready for world domination.

I can't find a shot of full grown plants in our current set up, but I did find a shot from 2010:

The two large bins on the ends each have two tomatoes in them; the pot in the middle is an eggplant, and two eggplants in the middle planter. The tomatoes in the foreground is a yellow pear tomato in an 11" pot, and I think that's a tomatillo between the yellow pear and the first planter.

The yellow pear in a pot:

The planters were okay, but we found we prefered the individual pots, and the plants do as well or better.

(The deck and door in these pictures have been replaced, so mind not the splintery deck ...)

What can be the largest pot what tomatoes roots take the whole volume of it? How far can tomato roots can spread and how deep they may grow? I red that all they need is 12" on the one hand while in another source I read that they may grow 6' apart!