Each airline has its own weight restrictions. The standard weight for checked bags is usually 50 pounds. Weight limits for carry-on bags typically range from 15 to 70 pounds. For example, the carry-on weight limit for bags on U.S. Airways is 40 pounds and 11 pounds for Air France, according to Luggage Pros.
While airlines don't put a specific weight limit on passengers, they do require passengers to purchase a second seat if they can not fit comfortably into one seat, according to a 2009 CBS article. United Airlines and Southwest Airlines are two airlines that carry this policy. According to Smarter Travel, when a passenger cannot lower an armrest on Southwest Airlines due to weight, he or she is required to purchase a second seat.
For both checked luggage and carry-ons, most airlines will allow you to surpass weight restrictions for an additional fee. In addition to weight, you should note that airlines also place restrictions on the dimensions of bags.
