Each person needs 23.5 in of table edge and about 16 in of table depth for a place setting.
That is why a dining table for two rows of guests is normally 31.5 to 35.5 in wide: two place settings plus room in the middle for dishes. At 23.5 in per person there is room to eat without touching elbows; at 27.5 in the table feels generous, and chairs with armrests need that much to pull in side by side.
The width of the chair matters less than you might think. Our slimmest chairs, Bella and Isabell, are 16.9 in wide, and the gap they leave is what makes 23.5 in comfortable. Sella and Erik, with armrests, are 19.7 in and 21.3 in wide and need the full 27.5 in.