<P> These are lists of the busiest airports in the United States, based on various ranking criteria . </P> <P> The FAA uses passenger boarding for a full calendar year to determine Airport Improvement Program (AIP) entitlements . The term hub is used by the FAA to identify very busy commercial service airports . For instance, large hubs are those airports that each account for at least one percent of total U.S. passenger enplanements . Medium hubs are defined as airports that each account for between 0.25 percent and one percent of the total passenger enplanements . According to preliminary FAA data, in 2014 there were 30 large hubs and 30 medium hubs . </P>

Which is the biggest airport in the usa