How big can a person be for plane seating?

Airline seating sizes can vary, but generally, the average economy class seat width is about 17 to 18 inches. Airlines often have policies that require larger passengers to purchase an additional seat if they cannot comfortably fit within the space provided. Some airlines may also offer "extra comfort" or "premium" seating options with more room. It's advisable for passengers to check specific airline policies prior to travel.