-"I would have expected 1 plant per four square feet."
That is a 2x2ft sq., right?
You don't say if you plan to prune or how much?

I would say give them as much room as you can, until you can see for yourself -
1. IF you will prune
2. just how much room they do take up.

When I had a row garden, I would give each tomato plant 4ft. each way. I never pruned. Only watered and tried to keep them off the ground. Esp. difficult when they are loaded with fruit and the Sept. hurricane rains come.

To visualize this, That is one plant in each corner of a 4x4ft frame and nothing for another 4ft from each plant. By Aug. I could hardly squeeze in between the plants to harvest. I guess the plants were happy?

I would say give them as much room as you can, until you can see for yourself.

ps. If you plant in the shade - you won't need as much room ;-)

I planted a Bush Celebrity last year and did not prune (I don't think you're supposed to prune determinates). I would give it at least 4 sf (2x2) if not a little more.

I just put out 20 det toms at 1.2' spacing (20 in a 24 foot bed). Last year, I did 1 foot per on a trellis, and the pruning required was a little too harsh, in my opinion.