The United States is home to 672 airports with scheduled commercial services, but only ten of these airports account for around 35% of all flights. As demand for air travel continues to increase, airports across the country are busier than ever. However, there is one airport that stands out as the busiest of them all.

In this article, we will use data from OAG to explore the ten busiest airports in the US based on the number of seats available in summer 2025. We will also take a look at each airport’s most popular routes and the airlines that operate there.

Seattle-Tacoma International Airport (SEA)

Ranking first on our list is Seattle-Tacoma International Airport (SEA), with over 19. 6 million seats available in summer 2025. As the third-busiest airport on the West Coast, SEA serves as a major hub for both Alaska Airlines and Delta Air Lines, with a market share of 51% and 24%, respectively.

SEA’s most popular destinations over the past 12 months include Los Angeles International Airport (LAX), Ted Stevens Anchorage International Airport (ANC), Phoenix Sky Harbor International Airport (PHX), Denver International Airport (DEN), and Harry Reid Las Vegas International Airport (LAS). Delta Air Lines offers flights to various destinations from SEA, such as Seoul Incheon International Airport (ICN), Shanghai Pudong International (PVG), Taipei Taoyuan International (TPE), and Tokyo Haneda (HND).

San Francisco International Airport (SFO)

With over 19. 6 million seats available in summer 2025, San Francisco International Airport (SFO) ranks ninth on our list. In 2024, SFO was the 13th-busiest airport in the US, but it has since risen to the ninth spot. United Airlines is the largest carrier at SFO, with a market share of just under 50%. The airport’s busiest domestic route is to Los Angeles International Airport (LAX), while its top three international destinations are Taipei Taoyuan International Airport (TPE), London Heathrow (LHR), and Vancouver International (YVR).

Charlotte Douglas International Airport (CLT)

Ranking eighth on our list is Charlotte Douglas International Airport (CLT), with a total of 20. 1 million seats available in summer 2025. American Airlines is the primary carrier at CLT, with a market share of 70%. Some of the most popular domestic routes from the airport include Orlando International Airport (MCO), LaGuardia Airport (LGA), and Dallas/Fort Worth International Airport (DFW). American Airlines also offers international flights to destinations such as London Heathrow Airport (LHR), Madrid Barajas Airport (MAD), and Punta Cana International Airport (PUJ).

Harry Reid International Airport (LAS)

Las Vegas’ Harry Reid International Airport (LAS) ranks seventh on our list, with over 20.