Airline Metrics: Available Seat Kilometers

Photo provided by American Airlines

Ashwin Jadhav, a member of our AirlineGeeks team, will begin a new series this week highlighting some of the important metrics that airlines monitor on a daily, weekly, monthly, quarterly, and yearly basis to improve performance. From a passenger’s perspective, this series will provide an excellent insight on how these metrics affect the way in which you travel.


Available Seat Kilometers (ASK) or Available Seat Miles (ASM)* captures the total flight passenger capacity of an airline in kilometers. It is obtained by multiplying the total number of seats available for scheduled passengers and the total number of kilometers in which those seats were flown.

Airlines have to try to match supply with demand for passengers’ benefit. While shortage of seats will often result in higher airfare, excess capacity can lead to reduced margins due to higher fixed costs. So an increase in capacity is positive only if it’s supported by an adequate rise in demand for air travel.

*While miles are the preferred unit of measuring distance in the U.S., the rest of the world uses kilometers as units for measuring distance. In the aviation industry, kilometers are used more often than miles in formulation and analysis of metrics and key performance indicators.

How is it calculated?

Available Seat Kilometers (ASK) measures an airline’s passenger carrying capacity. It is:

seats available × distance flown

This number should be calculated per airplane, but is usually quoted per airline.

A seat-kilometer is available when a seat that is available for carrying a passenger is flown one kilometer. Seats that are not usable for various reasons are excluded.

Why is it important?

ASKs give airline senior management a clear indication of their capacity. Larger legacy carriers usually operate several types of aircraft with different seating configurations. Hence, the ASKs help qualify the total number of available seats and the amount each seat will fly.

ASKs are further used to calculate load factor, revenue per ASK, cost per ASK, and profit.

Simple Example

“Blank Airlines” operates one Boeing 737-800 aircraft with a capacity of 200 passengers between New York JFK and Chicago ORD. The distance between the two airports is 1,190 KM, which means that the ASK per leg flown is 200 (the available seats) multiplied 1,190 (the distance these seats can be flown).

Hence, Blank Airlines has 238,000 Available Seat Kilometers per flight leg.

Based on the frequency of this route per day and per year, the daily and annual ASKs can be calculated accordingly.

Real-World Quiz

Blank Airlines is a domestic U.S. carrier that operates a fleet of 10 aircraft between major cities in the country. The aircraft, capacity, city-pairs, and distances are given below. Assuming that the aircraft operates for all 365 days in a year and assuming that all seats in the entire fleet are usable for carrying passengers, what will be the ASKs per year for Blank Airlines?

Aircraft Capacity City-Pair Frequency (+ Return Legs) Distance (KM)
Boeing 737-800 202 JFK-ORD Daily (4x) + (4x) 1,188
Boeing 737-800 210 JFK-MIA Daily (4x) + (4x) 1,757
Boeing 737-800 240 JFK-ATL Daily (4x) + (4x) 1,223
CRJ700 68 JFK-IAD Daily (6x) + (6x) 365
CRJ700 68 JFK-PHL Daily (6x) + (6x) 151
CRJ700 68 JFK-YUL Daily (6x) + (6x) 535
CRJ700 68 JFK-CLT Daily (6x) + (6x) 871
CRJ700 68 JFK-BOS Daily (6x) + (6x) 300
A330-300 390 JFK-LAX Daily (2x) + (2x) 3,975