for greenhouse tomatoes, at least in commercial structures, the winter spacing is 20% more than in summer.

What's the summer spacing?

Maybe I should clarify my question a little more.

I grow my tomatoes vertically at the back of my 4x4 planter beds, 4 plants in one row, 1 foot space between each. When I go to plant them in the greenhouse, I'll have two 4x16 (or longer) beds, and I want to plant as many rows of tomatoes as I can. What space between the rows can I get away with without them shading each other?

With a goal of maximum fruit production per square foot of greenhouse area, many research trials have been conducted comparing different spacings. Having more plants does not necessarily produce more fruit, per area. The optimum for indeterminate greenhouse varieties of tomato is 4 sq. ft. per plant summer, 5 sq. ft in winter. Closer spacings have more plants, but the production is not greater. The reason is shading from overlapping leaves. The plants are usually placed in double rows 14 inches apart, with the plants within the row 16 inches apart. Extra space is allowed for harvesting walkways between the sets of double rows. The actual configuration can vary, as long as the resulting individual plant spacing is 5 sq.ft in winter.

Much grass. That is exactly what I need.