Load factor in aviation is a measure of the stress to which the structure of an aircraft is subjected, and it is defined as the ratio of the lift of an aircraft to its weight). It is a dimensionless ratio, but its units are traditionally referred to as "g" because of the relation between load factor and the apparent acceleration of gravity felt on board the aircraft). A load factor of one, or 1 g, represents conditions in straight and level flight, where the lift is equal to the weight. Load factors greater or less than one (or even negative) are the result of maneuvers or wind gusts).
The lift in the definition of load factor is not simply that generated by the aircrafts wing, but it is the vector sum of the lift generated by the wing, the fuselage, and the tailplane). The load factor is closely related to the total acceleration felt by the aircraft, which is measured in "Gs".
The load factor is also used as a metric in the airline industry to measure the percentage of available seating capacity that has been filled with passengers. A high load factor indicates that an airline has sold most of its available seats and is preferred over a low load factor. The higher the load factor, the more an airline can spread its fixed costs amongst passengers.
