Note the Fleur arms which allow the arm chairs to be pushed in farther than our standard arms.
24" of width is best. A place setting is 20" wide, but the person needs more room than that. Typically chairs are 18-21" wide, but the person needs more than that.
From the front edge of the chair allow at least 14" for legs and knees when a person is sitting at the table.
So three on a side is 24" times 3 which equals 72", plus 14" on each end for a total of 100"!