Most chair widths are given in center-to-center dimensions. So a chair "22 inches wide" is measured from the center of one armrest to the center of the other armrest. So you multiply the number of chairs times the width. So, 3 chairs at 22" center to center equal 66". That's fine, but that is not the total length. You now have to add the other half of the armrests, at the ends of the row. This is usually 4 inches. So in the example, 3 X 22" = 66" + 4" = 70" total. Note this quote: From the Richmond Times Dispatch Apr 16, 2005 BY CLARKE BUSTARD. "Seats in the historic movie palace in Carytown are 18 inches wide, the same as an economy-class seat in the Boeing MD-80 flown by American Airlines. And there's less legroom: 27½ inches from the back of a seat to the back of the seat in front of it at the theater, compared with 31 to 32 inches on the plane."... "To compare these dimensions with those of your body, sit down and measure the width of your lap and the distance between the back of your hips and the front of your knees.