The definition of world's busiest airport has been specified by the Airports Council International in Geneva, Switzerland. The ACI defines and measures the following three types of airport traffic:
Passenger traffic: total passengers emplaned and deplaned, passengers in transit counted once
Cargo traffic: loaded and unloaded freight and mail in metric tonnes
Traffic movements: landings and take-offs of aircraft
The following airports make claims based on objective volume measures that are defined above (as per ACI):
Hartsfield–Jackson Atlanta International Airport, Atlanta, Georgia, United States
Most passengers annually (1998–2013, 2015–present)
Most aircraft movements annually (2015–present)
Dubai International Airport, Dubai, United Arab Emirates
Most international passengers annually (2014–present)
Hong Kong International Airport, Hong Kong, China
Most cargo traffic by weight annually (2010–present)
Airports of London combined, London, United Kingdom
Most passengers annually in all city airports combined (2010–present)
Chicago Midway International Airport, Chicago, Illinois, United States
In the late 1940s, Chicago Midway was the busiest airport in the United States by total aircraft operations – i.e., including every training aircraft practicing take-offs and landings. New York LaGuardia had the most airline operations and passengers until the early 1950s, when Chicago Midway became the busiest airport in the United States by any criterion. Before World War II, Chicago Midway was the origin or destination of one in four U.S. airline flights, although a 1939 Official Aviation Guide shows more airline flights scheduled at Newark than at Chicago.
Memphis International Airport, Memphis, Tennessee, United States
As the home of Fedex Express, Memphis had the largest cargo operations worldwide from 1993 to 2009. It remains the busiest cargo airport in the United States and the Western Hemisphere.
Non-standard claims
Gatwick Airport, London, United Kingdom
Gatwick has the world's busiest single-use runway. It does have two runways on site but the close proximity of the two and the length and lack of guidance for the second means that only one is used.
Wittman Regional Airport, Oshkosh, Wisconsin, United States
Wittman Regional Airport typically does not receive an above average amount of air traffic, however, for one week a year it is the busiest airport in the world in terms of amount of air traffic. The event EAA AirVenture Oshkosh typically begins on the last Monday of July, and brings in tremendous amounts of air traffic during that time.
