The size of an airline seat varies depending on the plane model and its seating configuration. A coach seat on a commercial airline is 17 to 19 inches wide, on average. First-class seats are customarily 21 inches wide.
These numbers are deceptive though, since they are based on the width of the seat cushion. In first class, the armrests are wider by 3 to 5 inches, making the seat feel roomier. The Airbus A330 has the smallest seats, measuring only 16.7 inches across. In contrast, the double-decker Airbus 380 boasts at least 19 inches of side-to-side space for every passenger.