ASK and RPK explained: airline capacity and traffic

Available seat kilometres (ASK) measure an airline’s passenger capacity; revenue passenger kilometres (RPK) measure the traffic it actually carries. One ASK is one seat offered for sale and flown one kilometre. One RPK is one paying passenger flown one kilometre. Airlines use them to size their operations and as the denominator for unit revenue and unit cost.

Explainer · Definitions checked on 6 October 2026. Tables update automatically with the airline database.

How to calculate ASK and RPK

ASK = seats available × kilometres flown

RPK = paying passengers × kilometres flown

An aircraft with 180 seats flying a 1,000 km sector produces 180 × 1,000 = 180,000 ASK. If 153 paying passengers travel the full sector, it generates 153 × 1,000 = 153,000 RPK. Dividing RPK by ASK gives the load factor: 85%.

Airlines add up every sector to report network totals, usually in billions. US airlines report the same measures per mile: available seat miles (ASM) and revenue passenger miles (RPM). One mile is 1.609 kilometres, so ASK equals ASM multiplied by 1.609.

Why ASK matters

• Size and growth: ASK growth is the standard measure of how fast an airline is expanding capacity.
• Unit economics: revenue and costs divided by ASK give RASK and CASK, which make airlines of different sizes comparable.
• Load factor: RPK divided by ASK shows how much of that capacity was sold.

How airlines plan capacity

Capacity is the product of four choices: how many aircraft fly, how many seats each carries, how many hours a day each flies, and how far each flight goes. Airlines plan it seasons ahead, balancing demand forecasts against aircraft deliveries, crew, airport slots and maintenance. Adding capacity faster than demand usually pushes fares and yield down; cutting capacity can support fares but leaves fixed costs spread over fewer ASK, raising CASK.

The same ASK growth can therefore be healthy or harmful. Our growth tracker compares capacity growth with unit revenue and margins, and the fleet and orders data shows the aircraft behind each airline’s plans.

Largest airlines by capacity (ASK, latest full year)

Airlines that report capacity in ASK for their latest full year, from company reports. Group figures include several airlines and appear alongside some of their own subsidiaries.

Latest full year reported by each company in our database (25 airlines). Fiscal years end in different months; "Group" figures cover a wider business than one airline. Figures are not converted or estimated. Updated automatically when the airline data is refreshed.

Airlines reporting in available seat miles (ASM)

US and some Americas carriers report capacity in miles. These figures are shown as reported, not converted.

Latest full year reported by each company in our database (12 airlines). Fiscal years end in different months; "Group" figures cover a wider business than one airline. Figures are not converted or estimated. Updated automatically when the airline data is refreshed.

Common questions

What does ASK stand for in aviation?

ASK stands for available seat kilometres: the number of seats available for sale multiplied by the kilometres flown. It measures an airline’s passenger capacity.

What is the difference between ASK and RPK?

ASK measures capacity offered; RPK (revenue passenger kilometres) measures traffic carried, counting only paying passengers. RPK divided by ASK is the load factor.

How do you convert ASM to ASK?

Multiply available seat miles by 1.609, because one mile is 1.609 kilometres. For example, 100 billion ASM is about 160.9 billion ASK.

What is airline capacity planning?

Capacity planning is deciding how many seats to fly on which routes and when. It combines fleet size, seats per aircraft, aircraft utilisation and sector length, and aims to match supply to demand at fares that cover costs.

Related explainers and data

• Airline load factor
• Airline yield
• Break-even load factor
• RASK and CASK
• Airline comparison tool for company-reported figures across more than 100 airlines