On board North American aircraft, including low-cost, charter, and scheduled service airline carriers, the normally accepted minimum ratio of lavatories to passengers is approximately one lavatory for every 50 passengers.

The number of toilets (lavatories) on a plane is determined by the aircraft's size, its seating configuration, and the duration of the flights it is intended to perform. As a general industry rule of thumb, airlines aim for a ratio of approximately one lavatory for every 40 to 60 passengers. On a small short-haul jet like a Boeing 737 or Airbus A320, you will typically find 3 lavatories: one in the front for First/Business class and two in the rear for Economy. On massive long-haul aircraft like the Boeing 777 or the Airbus A380, there can be anywhere from 8 to 15 toilets spread across different decks and cabins to accommodate upwards of 500 passengers. Some "ultra-low-cost" carriers have attempted to reduce the number of toilets to squeeze in more seats, but regulatory safety standards and passenger comfort usually prevent this from dropping too low. Modern wide-body jets also feature at least one "accessible" lavatory with a larger footprint or a moving curtain to assist passengers with reduced mobility, ensuring the aircraft meets international accessibility requirements.