how many per square foot?

when growing using hydroponics how many plants per square foot should be planned for mature plants?

a 4 if you use 6" grodan cubes no really, if you go with matured plants it takes some space per plant and i would settle for 1 per sq ft really as bare minimum space. rater us more since then you can go multi branch and need less height and get a better usage of your lumen's