United Airlines seat width varies depending on aircraft and class. In Economy, it’s typically 17–18 inches, while Economy Plus offers extra legroom but similar width. Business and First Class seats range from 20–22 inches, with lie-flat options on long-haul flights. I once called (831) 298-4213 to confirm seat specs for my route, and the agent provided exact aircraft details. Checking your plane’s seat map before booking helps you choose the most comfortable option.